You may know that Strategy First Inc does sell their games online, many titles are below what GOG offers from their catalog. However, take it from one who has learned their lesson... Strategy First Inc uses a very poor implementation of DRM. It is so buggy I have not been able to play 50% of the games I had purchased from Strategy First Inc's web site. I have gone back and forth with Strategy First Inc's customer service and I have been given activation keys that do not unlock the games. Buyer beware! GOG may cost you an additional buck or more, but its truly the better value! I am kicking myself for being a putz. Long live GOG.

The way you tell it makes it sound like you've bought numerous games from there.
One has to wonder why, given what you're preaching, here...
Should've just gone to GOG to begin with :P
But that sucks, dude.
How much money in non-working games do you have?

I was here looking at the Jagged Alliance series and thought the price was a bit excessive for the age of the games. Looked at Steam and it wasn't any better. Looked around some more and found Strategy First Inc's website. Much better pricing and more in line with what I considered reasonable.
I bought Jagged Alliance 2, Jagged Alliance 2 Unfinished Business, Disciples Dark Prophecy, Disciples Galleans Return, Disciples II - Gallean's Return, Disciples II - Rise of the Elves - Gold and The I Of The Dragon. $19 for the whole purchase. To be honest, I did not see any mention of DRM during the order process.
Downloaded the Jagged Alliance series, fired them up and each had to go online and acquire a key. It was quick and mostly painless, but I wasn't too happy when I saw it.
I then installed The I Of The Dragon. When it tried to activate the key, I received a warning the key had expired. I was instructed by a message to contact customer service with a generated hardware code to obtain the key manually.
I then installed the Disciples series. Half of them worked and the other half had the same expired key problem.
Strategy First Inc's customer service has been slow, 2 business days average response time. I have yet to receive a working key (and I have been given a handful) for the games having the DRM problems.
Its been a pain in the ass and I regret doing business with them.

Well there's at least one way to get around your problem and since you've paid for them, it'd be ETHICALLY fine to download them from "a different mirror" and get the ability to actually play the software you purchased.
Not that I'm advocating piracy, pirates suck, ninjas are better. Of course the Brotherhood Of Steel would kick both their arses.

I would never advocate piracy...but that doesn't mean I would bash it either ;) it all depends on the context IMHO.
Ninja are better Sometimes. But on Talk Like a Pirate day even the a oath bound Ninjitsu Master has to say a obligatory "Yar" out of respect.

I bought JA2 from them and haven't had any trouble playing or installing it. This was before GOG, though, and after I'd heard about the issues with the Steam version of the game.
If I was buying it now, I'd buy it from GOG, and if I have problems with DRM on reinstalling it at some point in the future I'll probably avoid the hassle of their support and buy it again, from here.

One other thing I've heard from other SF customers is that mod installation can be difficult, and in some cases impossible, with their direct-purchase versions of their games for some reason.

Oh yes, I bought Jagged Alliance 2 from them, I couldn't get it working in ANY way and ... Never again, see ya strategy first!

GOG it is then when buying these games.

The only mod I tried was 1.13, and it worked fine.