a looong time ago, i was wondering the same thing. then i found out that they can cause
burns on birds' feet after extended use or something. i'd advise against them, but that's
just me.
I have been using one for several years. Never had a problem with the temp. Problem was my bird developed pressure areas on her feet as it is a hard plastic material. I wrapped it in vet tape and have had no further problems with it. Birds love them.
I suppose it's like anything else. You need to keep your eye on it in case it does malfunction. Everything breaks eventually; sometimes it just stops working and sometimes it goes haywire