Well, you can't let them sit for a long time with out working.
They do provide some mediocre blades. But, as long as you avoid rocks, & let the knifes work the rubber, it's great.
I've cut up at least 3 sets of 38's, & still have plenty of the original blades that came with my order. I think I used up 2 blades on a set of 39.5 IROKS.
I also picked up an extra head, for a wider cut.
Preheating makes all the difference in the world.
I've seen guys shave off complete lugs before, by heating up a chisle until it glows, & heat the rubber. Cut the whole lug out completely.
Anyway, I recommend you get your own set up if you do a lot of wheeling. $100 sets you up for quite a while.