In reply to Howard J:
> I'm puzzled by the policy some walls apparently have of requiring customers to belay with devices they're not familiar with. Surely this is more dangerous?
I think you are correct that is safer belaying with a device you are familiar with. The problem the wall has , its " wall police " need to able to tell at a glance if everything is ok, a simple blanket standard is easier to check.
As an example , I use a bowline or figure eight, my mate use a Yosemite bowline, to me I have no idea if he has tied it correctly, I assume he knows what he doing and tied right or wrong it looks like it would work; not really good enough for insurance companies !