I had a mechanical one, but I realized it was off. Tick-tock, tick-tock instead of tick tock tick tock.... I haven't trusted them much after that. But that's just this one old mechanical metronome. I figure the electric one can't do that. It would just shut off.
I'm shameful to say I've never own a metronome from the very first day studying piano.
Mmm... Still need loud. Cheap ones aren't that loud.