In my previous trailer and present trailer both had the N641 Norcold units. (2 way) So far they have worked as expected. I would purchase another one. I wouldn't bother with the 3 way unless you had a fancy solar system to recharge the batteries.
I have found the efficiency is better after I placed a small battery operated fan on the interior and on days when it gets very hot 90+ degrees I place a small fan in the rear.
The automatic switch over from elec to gas has worked flawlessly.
My only complaint is that the previous owners should have installed the N841 instead.
Steve, Christy, Anna and Scout (Border Collie)
1994 30'11" Excella - rear twin
2009 Dodge 2500, 6 Speed Auto, CTD, Quad Cab, Short Bed
Hensley with adjustable stinger
WBCCI # 3072
AIR # 6035