However, when lead belaying, you need to pay out rope, which means disengaging the auto brake. If you do this buy holding the handle and the climber falls at the wrong time, it's easy to react by just holding everything tighter, at which point you're holding the grigri open, at which point the auto brake isn't doing anything. By contrast with an ATC or other tube-type device you never have to touch the belay device and so you always can keep your brake hand in the brake position, so if the climber falls, your reflex action -- assuming you have practiced -- should be to pull harder with your brake hand, thus arresting the fall.
Aside from belay devices, some other practices I've seen gyms do to try make indoor climbing safer:
- Captive grigris on top rope so that you (1) have to use a grigri and (2) can't screw up putting them on and off. - High friction toprope anchors (e.g., wrapped several times around a pipe) so that even with no belay device at all there is still some friction. - Requiring people to tie in with a trace eight rather than a double bowline on the theory that the trace eight is harder to screw up and easier to check.