Yeah, this is something of a concern I have personally for these sort of abilities in general. Usually for a Battle Master Fighter, you can make the attack roll and decide to apply Battle Master maneuvers afterwards; it's hard to make that work in an engine like BG3, so instead you choose to do a maneuver when you choose to attack and afaik it just doesn't burn your maneuver dice unless the attack actually hits.
Doing it this way does affect gameplay, especially if they do the same thing for say Paladadin' Divine Smite. Fishing for crits with multiple attacks / advantage and then only activating your Smite after confirming a crit happens is a really strong way to boost your damage without blowing your spell slots too quickly. Similar thing for say the Defensive Duelist feat, where you can use your reaction to add your proficiency mod against an attack. There are a lot of cool abilities like that in 5E that give you an "A-ha, in reaction I do this!" option that doesn't work the same in BG3's engine. Hopefully Larian has a good way to work around the differences, though I wouldn't be surprised if it leads to abilities being reworked a bit, which is kind of a shame.
