I've had the 30" and 40", it's a natural evolution thing. I'd suggest bypassing the window - it's neat, but, doesn't add to the cooking capability, may be a heat-loss part of the smoker, and requires constant cleaning if you want to view through the window. Basically, it costs more, adds nothing to the cooking capability, and requires more maintenance.
I've had the
amnps since day one. When it works, it is wonderful. It works about 1/2 the time. After 5 years using it, I can not say that I've found any method to make it work consistently. It's a very nice add-on, since when it doesn't work all you have to do is keep feeding the chip tray - no big loss.
Keep your eye out for Rural King, Menards, Walmart, Orscheln's to have sales on the MES 40.
Good luck.