The 512 is the Gen 2 Black w/ Stainless Door and a lot of problem's. Of all the guys here that have commented I think only one said he was happy with it and had no Fire, Overheating or Controller issues.
The 311 is the Gen 1 All Stainless unit. Many of have this model and other than the occasional 20°+/- difference in set point temp from actual temp they work great. Not to mention the AMNPS will work perfectly no mods needed. I have 2 now, no issues...JJ