IME the 2012 Nexus 7s were problematic. I had three. The first (32GB wifi model) suffered massive slow downs which got worse over time. A factory reset and restore would fix it for a while. It's not an uncommon problem if you Google about. Lots of blame being placed on the cheap NAND being used.

My second was a 3G model. That just died on me one day out of the blue. The replacement had awful wifi reception. I'd get almost no signal while sat in the same room as the router. I sold that pretty quickly.

I'm still using a 2014 Sony z3 compact tablet which has been faultless. No slow downs. The only thing I'd wish for is that it had 32GB instead of 16GB. I've not put Sailfish on it though. It is in the libhybris list but too many red blocks and it's more useful as an Android tablet.