DannyD, you might be doing something wrong. In 15+ years of climbing, I've only had one of the units slip one time, when I was in a hurry descending (call of nature). Maybe you're putting your weight on it too quickly, before it bites the tree. Put your weight on it slowly, so if it isn't biting you're not slipping so abruptly.

My API came with a ratchet strap for the seat unit, to be snugged around the tree once you reach where you want to be. One more bit of security. I don't know if they come with them now, but you could probably rig one, just don't drill or cut the stand.

Gotta agree with all, love the climber.