I'm a long-time BP user.
But for this time, I wanted to try Stratagems on BG2:EE. But I was really disappointed.
When you encounter a Stratagems wizard, things are really difficult, much more than BP. But this is mostly the only challenge with Stratagems. The rest is painfully easy. Irenicus Dungeon, Copper Coronet, Sewers, Boat, Mae'Var, Tanner's Quest... All of this is mostly vanilla and bland. Stratagems seem to increases the difficulty only in some spots, like Tactics did.
Stratagems need that you install spell tweaks. Well, you can choose not to install them, but Stratagems AI will assume you have anyway. At least BP does not impose arbirtrary rules changes.
With BP difficulty is increased much more constantly. Wizards and Priests are not killing machines because they can -do mistakes-. And new creatures are added to increase the challenge.
To be honest though, maybe the numerous bugs that plague the last version of Stratagems (unfortunately with BG2:EE you can't play with regular SCS II) explains partially why the game was so bland most of the time. But v28 has been around for quite a long time now and the only SCS version available with BG2:EE.
Please don't let BP die because Stratagems exists. We need something different than Stratagems on the mod market.