Yes, have one as the only source of heat in our en-suite. Initial switch from totally cold is approx 1 minute to feel the heat (mounted at ceiling level). It's on a 15minute timer and if it's triggered repeatedly it feels warm quickly.
Not much use for a quick pee, but sitting down or having a shower gives it plenty of time to warm up. It'd be better if mounted on a wall as a mirror as the heat would be right next to you.