THe only problem is with the poly mounts you dont get all the new harware and what not that comes with the LMC kit. LMC rubber mounts keep more vibration out of the cab too. There are trade-offs either way. I think Rubber is better for the cab mounts for the comfort factor. It takes them a LONG time to wear out. By the time the do wear out you wont mind replacing them again. Our trucks are all about 20 years old and most on original rubber bushings.