There are many good recommends in this thread,
and GOG choose the WORST solution (maintain two sets of offline installers for each game).

Recent GOG offline installers have wrong checksum, wrong filename, wrong versioning, wrong UI language, wrong changelog. (All those problems occurred in this very year 2017)

GOG have made so many errors, and now they want to maintain even more installers?
I just do not trust them.

I have a simple solution for you: Don't trust if you don't want to. Wait and see.

Considering the change could be that only the .exe file is different (by ditching the innosetup and going back to encrypted rar files), it could very well be the best choice. Until the community starts yelling again that they can't use innoextract to extract the .bin files, and that the .rar files ask for a password that can be easily computed.

But just like ZFR said, wait and see.

It seems obvious to me that gog will slowly phase out the new "classic" installers just like they are doing with the GOGdownloader. Their reasoning will be that it's too difficult and costly to maintain both. The question is how long until this happens, months or years?

Of course I trust them; why wouldn't I?

They've done such a great job fixing the notification system, what's not to trust?

A lot of people on this forum need to remember that they're not the majority. You don't like, well that is just tough. They'll do what they feel is necessary.

What does encrypted rar files have to do with different .exe files, but otherwise yeah.

You're not the only one...

https://www.gog.com/forum/general/offline_installers_with_an_option_to_install_gog_galaxy/post571
https://www.gog.com/forum/general/offline_installers_with_an_option_to_install_gog_galaxy/post1039
https://www.gog.com/forum/general/offline_installers_with_an_option_to_install_gog_galaxy/post1060
https://www.gog.com/forum/general/offline_installers_with_an_option_to_install_gog_galaxy/post1114

I don't trust GOG to dress themselves in the morning.

Ok... Perhaps that's a little unfair. But I don't trust them with anything involving "coding" at all.

The reason for using rar files was so one could easily change the .bin files without having to hash everything again. The reason for encrypted (or password protected if you prefer) was so they couldn't be easily changed by malicious users, especially if people weren't getting them from GOG.
Not so sure how innosetup works, and whether changing just the exe file requires a full rehashing or not, but someone who knows more about innosetup could tell us if they could do the same without the rar files.

I don't actually know a huge amount about creating installers, but presumably it's not dissimilar to compiling code in general. In which case I would imagine creating the two separate installers would just be a matter of ticking the right box to create the installer, or something similar anyway (as the only difference is going to be a Galaxy installer in one).

I'm not seeing it being a huge deal really...

But GOG is GOG.
They can't still post working links after making the same mistake for years.
The devs probably have to start some wonky Goldberg machine to do anything :P

And GOG promo often have wrong countdown, mismatched date and time with the announcement post.
I think GOG staff just do not know what is timezone.

Poor darthspudius, he's been working overtime in the Pathetic Corporate Bootlicking Department for days now. GOG should hire more stooges to share the burden.