See what Bill (below) said. That pretty much covers it. Try to find a Gen #1 MES 40, and avoid the Gen #2.
The good one (Gen #1) has the controls in a little slanted box that attaches the the middle back of the top.
The one to avoid has the controls built into the top front edge.
my advice, don't buy the mes generation 2, if you can your hands on a Gen1 go for it. I had FIVE Gen 2's. Each one had problems from failing the seasoning process (2 failed) to temperatures being as much as 40 degrees too low, to leaking doors etc. Masterbuilt keeps putting bandages on these units, sending out replacement parts but won't address the problems and fix them. Can't successfully use an AMNPS in this model the air currents are all screwed up (just ask Todd at Amazing products). I finally got MES to take back the "512" model and send me a "311" 40". Amazon might still have the Gen 1 40". do yourself a favor avoid the Gen 2.