Before I evolved to SRT I tried just using my heliums, heliums with a couple Stepps and tried a ring with my old Ameristep strap-ons too. I had a kick out incident like rob mentioned as well, but it happened when I a cammed step on both sides of the stick so I was able to get it reset without any calamity. Was a little rattled tho.
Personally I didn't like just the helium, the step width is just too narrow for anything more than a couple hours, plus the kick-out potential. Camming a couple stepps more or less at the same level was a PIA to me too. The Ameristep strap-on's were easier to install but they aren't designed for side pressure and tended to shift and loosen as I pushed on them, just can't get them tight enough with the cam buckle. They would be better with a ratchet strap to tighten them enough. Maybe the squirrel steps are better.
Anyway, I much perfer my predator platform, very comfortable on your feet, holds tight to the tree and is just one thing to install.