In reply to mrphilipoldham:
I had them slip, off quite substantial holds, but then stick on marginal stuff, my mate found the same. They'd stick where you thought they might not, but then slip on stuff you wouldn't dream they could, very strange.
They make for interesting climbing, I've been looking for a replacement for my Mad Rocks (C4) since I'm not sure how many resoles a shoe can actually take. Jokers aren't the ones for me.