It's kinder to be soft with a stronger bit than it is to be strong with a bit that's too soft.
If you like the methods your trainer uses for other things, I'd take her word for it on this bit and give it a try. Watch his reactions... if you apply it does he comply or does he fight and throw his head? One thing is, with a curb bit, you don't want to ride on contact with his mouth all the time like you can with a snaffle, you want to ride on a looser rein and apply the bit in pull and release motion as needed.
Pulling and releasing. Boy, do I know that routine. Sarah Lee just wants to get faster and faster. I have to really work to keep her at the same speed. The trainer says, I'm training her and she's learning. I'll just have to take her word for it. That she horse has got such a smooth, comfortable jog but she likes that trot that bumps my kidneys and brain together:') I found another speed she can go now though. The trainer called it a trail ride walk. I liked that one too. She must have at least 5 gears in each gait!