That polybutylene really is crap! I had to move the toilet supply line a bit (also made of PB) and the damn brittle stuff snapped off at the shutoff valve. Had to make an emergency trip to the hardware store. I cut off that whacky shutoff valve with the spring in it that you have to push in and turn at the same time. Got a nice 1/4 turn shutoff and braided supply.
BTW, those smaller white compression fittings work fine for the 1/2". They just need that additional insert for the 3/4", which the guy at the hardware store neglected to tell me the first time around. But, I'll still use the Qest for underground repairs.