I'm not sure with lizards but am guessing they'd be fine as they like it hot.Some people swear against hot rocks and some people use them and breed successfully.I would put one on a thermostat if you can though as they can get really hot.I've used them before and they worked well.
I use a 6watt heat rock for both my blueys and water dragons and have no problems at all.. They wander on and off all the time. The way i see it is if it is too hot for them they will move away.
I use one with my gecko. I've stood it up on its end and lent it against the wall. Then I have a big bit of bark standing beside it. That gives Zeus a hidden, vertical warm surface to sit on. He spends all day there and comes out at night.