i recently picked up the o rings, primarily for my pf trains. i'm still digging through this forum to find additional evidence of this concept's success for pf, not that i doubt it works, just not sure the fiddling is worth it if the improvement is minor. i couldn't get the o rings off with my fat fingers. now i have to find a suggested toothpick or something similar to remove the old ones. i definitely see slippage in my pf trains when adding a few extra cars. i had to replace most of the magnets first as those new ones didn't seem to hold together well with extra cars. Of course my 10 yr old figured out that you could use a 1x2 plate and connect the magnets. i must have missed that. i didn't even know the 9v's had the o rings as well. If i find that I can get the o rings off of both types easily without destroying them, I'll test and report back but don't hold your breath.