The no-cut ones are junk. Some bikes, like my old yzf 600r, didn't require it anyways. Most bikes require cutting, some companies make no-cut frame sliders for said bikes, but have heard in many cases they don't do their job.
Make sure they are made outta something like Derlin, they hold together pretty well in a fall but not well enough that they hurt the bike. I haven't heard about the no cut ones not working, but it could be that they dont attach to the frame due to the no cut.