The Trainer crashes if you use it more than 2 or 3 times, I play with scripts and got about 3 crashes in ~15 hours playing. If you don't use hundrets of scripts and only one or two PROFERSSIONAL ones (not self-made but tested and well-made), it should be okay!
1. You can't know it (not unl. member and you can't get the trainer)
2. Nobody have that problem and even you don't need to reactivate it. (same function as script activate one time per start is enough, and with trainer you still can disable it with script you must exit game->edit files->start game)
3. The scripts which were downloaded from GTA Forum from GTA Sunny Builder team crashes the game (they are professional enough i think)
Just stop compare things which are completly different.
It's like when you compare Bus with Truck that are completly different things.