Hold Fast Straps

If powergrips are set up correctly you shouldn't be able to release by pulling straight back....you're supposed to have to twist out slightly due to them being mounted diagonally.

Thats also part of the problem when it comes to tricks/polo, it makes them harder to escape from than horizontal straps, which means you are less likely to get your feet out when bailing/crashing which is inevitable in both tricks and polo.
Personally I prefer these massively to power grips, and every single person who has ridden them says the amount of extra leverage you can generate with these compared to power grips is much better, making stopping/skidding/hopping etc much easier, not just because they are wider, but because they also have four contact points with the pedals, as opposed to two (power grips).