Small crockpot for cheap humidifier?

[ValorieBoyer]

My mother in law uses a small "dipper" sized crock pot as a cheap humidifier solution for the plants in her living room. She has it set on a table next to a large group of them and keeps it filled to the top, on the warmer setting and says it works wonderfully. I'm a little leery about this (fire hazard cuz it's not meant to run that long so constantly? bump it and water goes everywhere?), has anyone ever used this method?