The oven I have is a HotLogic mini -
. It looks just like an insulated lunch bag, but, has a cord sticking out. It heats things really slowly, but then holds at serving temp ~forever. It is a lifesaver in hotel rooms for me mostly, as I travel a lot for work and get sick of eating out all the time, but still want hot food (so I use it for heating up lukewarm delivery, or heating up leftovers, etc). Several times FAs have noticed it and applauded me (or even told me they have one themselves, I think it is a fairly well known brand for those on the road a lot). But it pretty clearly looks against the rules ... I didn't realize that actually, since it just plugs in to standard power and has no exposed heating element, I thought it was relatively safe. I enthusiastically endorse it though in general, particularly if you spend a lot of time in hotels (or even for use at the office to heat up lunch, etc).