Ive replaced hubs, wheels, headlights, bars and then some from hillclimbs with a twist grip. You cant let off the throttle on a steep hill when you are holding on. When you land a jump your wrist is naturally going to drop down and give it gas. When you are trail riding, you are hitting rutts and and hills while tryin to turn. You will be giving it gas when you dont want to and letting off when you dont want. Let alone if you have to grab the front brake hard, you are going to twist the throttle when you squeeze the brake.
I put it on and hated it after the first ride. I have the thumb throttle again now.