Given that feeling (which seems to be shared amongst many people with even a cursory look at the forums) does it make sense/is it even safe to continue to invest in buying games from them?

It's a decision that everyone needs to make for his or her self. Note that GOG has been moderately incompetent since day one, especially in technical and PR matters. It's nothing too new. But it does seem to have gotten worse in the last couple of years --- perhaps just because GOG is larger now.

All I can say is that I bought exclusively from GOG from 2009 to 2020 (my library is close to 2,000 items), whereas in the last year, 98% of my DRM-free/client-free purchases have been on steam (and its key resellers).

Insomnia deals so far + predicted upcoming (2022-06-26 17:00 UTC):

Past:
(see here)
60. Dungeons 3 [EUR 29.99 -> 9.00 (-70%), 48/300 sold]
61. Opus Magnum [EUR 19.99 -> 8.00 (-60%), 48/300 sold]
62. Interstellar Space: Genesis [EUR 27.99 -> 7.00 (-75%), 57/300 sold]
63. Two Worlds II: Epic Edition [EUR 18.79 -> 4.69 (-75%), 59/500 sold]
64. Narita Boy [EUR 24.99 -> 7.49 (-70%), 52/500 sold]
65. Unreal Tournament 2004 Editor's Choice Edition [EUR 9.39 -> 0.99 (-90%), 498/500 sold]
66. Vampire: The Masquerade - Shadows of New York [EUR 10.79 -> 2.19 (-80%), 223/500 sold]
67. Webbed [EUR 8.19 -> 5.79 (-30%), 54/500 sold]
68. Two Worlds Epic Edition [EUR 9.39 -> 1.39 (-85%), 221/500 sold]

Current:
69. Dreamfall: The Longest Journey [EUR 14.09 -> 4.29 (-70%), ?/500 sold]

Upcoming:
70. System Shock(TM) 2 [$9.99 -> $? (-?%), ?/? sold]

If the purchases are on steam, how are they drm & client-free? I presume steam installed and then played directly w/o steam? If so, how do you know ahead of time if it is one of the games that will work that way?

Insomnia deals so far + predicted upcoming (2022-06-26 18:00 UTC):

Past:
(see here)
60. Dungeons 3 [EUR 29.99 -> 9.00 (-70%), 48/300 sold]
61. Opus Magnum [EUR 19.99 -> 8.00 (-60%), 48/300 sold]
62. Interstellar Space: Genesis [EUR 27.99 -> 7.00 (-75%), 57/300 sold]
63. Two Worlds II: Epic Edition [EUR 18.79 -> 4.69 (-75%), 59/500 sold]
64. Narita Boy [EUR 24.99 -> 7.49 (-70%), 52/500 sold]
65. Unreal Tournament 2004 Editor's Choice Edition [EUR 9.39 -> 0.99 (-90%), 498/500 sold]
66. Vampire: The Masquerade - Shadows of New York [EUR 10.79 -> 2.19 (-80%), 223/500 sold]
67. Webbed [EUR 8.19 -> 5.79 (-30%), 54/500 sold]
68. Two Worlds Epic Edition [EUR 9.39 -> 1.39 (-85%), 221/500 sold]
69. Dreamfall: The Longest Journey [EUR 14.09 -> 4.29 (-70%), 105/500 sold]

Current:
70. System Shock(TM) 2 [EUR 9.99 -> 1.99 (-80%), ?/500 sold]

Upcoming:
71. Machinarium Collector's Edition [$14.99 -> $? (-?%), ?/? sold]

My limited experience with steam:

0. I have a steam library of ~230 games, almost all of them DRM-free and client-free (or -freeable). It's small compared to my GOG library (~2300 games and demos), but mostly because for many years I was under the impression that steam's client was mandatory (which it is not). I have bought only GOG games from 2009 to 2020, beginning to buy on steam only in 2021 (primarily because games there are often much cheaper (when sold in bundles) and more likely to be kept up-to-date, while still being DRM-free and client-free).

1. I have never installed the steam client (I don't like GUI clients, or GUI interfaces in general). I use a command-line tool called SteamCMD (like a dumbed down gogrepoc, which is what I use for GOG) to download and install games, which I then backup. I play only from the backups (just like I do for GOG). I don't consider command-line tools to be clients, as they are essential for being able to maintain one's library updated. I don't believe it's feasible to maintain it manually via a web browser, not for large libraries such as mine, so having that option on GOG is almost meaningless for me.

2. As for the question of knowing whether a steam game is fully DRM-free or client-free ahead of time, it is indeed something of an issue (as it is for GOG games too, to a lesser degree). There are lists that people and websites maintain of such games, but they are woefully incomplete. I had looked at them initially, but don't bother any more. I do, however, check the steam game page, as steam does often (but not always) list major DRMs, such as Denuvo, there. It's my experience that only a small portion of steam games cannot be played without the client (i.e. the vast majority can). Of the ~230 games I have on steam, only two (2) proved unplayable without a client (one had DRM added after I had purchased the game; one could not be downloaded without the client due to misconfiguration). That's a much much lower percentage than that of (steam and GOG) games I had bought and then abandoned because I ended up not liking them (or simply did not work on my PC). So my impression is that while it is a valid theoretical issue, it is not --- for me --- a practical one. Mind you, I'm not really interested in new AAA games, many of which are presumably DRM-protected, but then these are for the most part not available on GOG either.

3. When I say client-free or DRM-free, I don't necessarily mean free out of the box (hence the -freeable above). In my limited sample, about 60% are so out of the box, the rest requiring some trivial non-game-specific modification (see below).

4. I use two tools to modify steam games that are not client-free or DRM-free out of the box:
- The goldberg DLLs (a pair of DLLs (32-bit and 64-bit) that replace the game's corresponding steam_api/_api64 DLLs, to remove client dependencies, such as achievements or cloud saving or DLCs or multiplayer, not related to DRM)
- The steamless program (an application that removes basic steam DRM from game exes)

5. My procedure for testing a steam game:
- try it as is; if works, done (about 59%)
- if not, try the goldberg DLL; if works, done (about 25%)
- if not, try steamless, with/without goldberg; if works, done (about 15%)
- if not, give up and ignore the game (only 2 so far) --- if possible, get a refund

6. So, to summarise:
- 84% of my steam games were DRM-free out of the box (and an additional 15% were easily made so)
- 59% of my steam games were client-free out of the box (and an additional 40% were easily made so)

7. Details:
SteamCMD can be found here: https://developer.valvesoftware.com/wiki/SteamCMD
Goldberg can be found here: https://mr_goldberg.gitlab.io/goldberg_emulator/
Steamless can be found here: https://github.com/atom0s/Steamless/releases

The games are not tied to the store. It wouldn´t make sense if I bought games from other stores with programs and servers tied to the games.

Thanks for this, it's interesting and seems useful.

Would you mind explaining more about the backup you create? I guess not all games are contained in a single folder that can be easily zipped, some will write values to the registry or whatever, so how do you deal with all that in order to get a full backup?

Insomnia deals so far + predicted upcoming (2022-06-26 19:00 UTC):

Past:
(see here)
60. Dungeons 3 [EUR 29.99 -> 9.00 (-70%), 48/300 sold]
61. Opus Magnum [EUR 19.99 -> 8.00 (-60%), 48/300 sold]
62. Interstellar Space: Genesis [EUR 27.99 -> 7.00 (-75%), 57/300 sold]
63. Two Worlds II: Epic Edition [EUR 18.79 -> 4.69 (-75%), 59/500 sold]
64. Narita Boy [EUR 24.99 -> 7.49 (-70%), 52/500 sold]
65. Unreal Tournament 2004 Editor's Choice Edition [EUR 9.39 -> 0.99 (-90%), 498/500 sold]
66. Vampire: The Masquerade - Shadows of New York [EUR 10.79 -> 2.19 (-80%), 223/500 sold]
67. Webbed [EUR 8.19 -> 5.79 (-30%), 54/500 sold]
68. Two Worlds Epic Edition [EUR 9.39 -> 1.39 (-85%), 221/500 sold]
69. Dreamfall: The Longest Journey [EUR 14.09 -> 4.29 (-70%), 105/500 sold]
70. System Shock(TM) 2 [EUR 9.99 -> 1.99 (-80%), 202/500 sold]

Current:
71. Machinarium Collector's Edition [EUR 14.99 -> 4.49 (-70%), ?/500 sold]

Upcoming:
72. Port Royale 4 [$39.99 -> $? (-?%), ?/? sold]

Machinarium Collector's Edition is showing the same price/discount on both the summer sale and the insomnia deal. So no bonus or point to it really. As in, both sale and deal are 70% off...

Yeah that's right GOG, don't bother dropping a nuke surprise or a keaning...

Thank you so much for the information/tutorial. This is very helpful. (Yeah, command line tools are not clients) I've done what you've done for another service except that I use the client to download initially, then backup/run it w/o the client (typically needing no goldberg or steamless equivalent). I'll have to look for a steamCMD equivalent for the service. Thank you again!

Yes. And that´s one of the reasons why it is so important to have a forum thread with the list of those games (lately, I haven´t been able to find the thread about the broken installers) and to constantly remind GOG about the need to fix the offline installers of some games.

Exactly. Which returns to schwartzag's original question ("is it even safe to continue to invest in buying games from GOG") and my answer ("It's a decision that everyone needs to make for his or her self"). Some people seem to think yes, some no.