I'm rather curious about this, too.

I'll chime in with what I've personally dealt with.

Both Aroma brand

Glass lid, metal cooking pan has a lip that rolls outside of the heating base. Just a simple switch, cooking & warm. Does boil over once in a while, and fairly small...ease of cleaning, really really easy.

Enclosed unit, has a metal pan that goes inside and a steamer basket, has a removeable metal top to clean...haven't had it for long, but I can imagine the seals will deteriorate and make it not as long lasting as the other pan...However, those seals do make cleaning more difficult.