The only real issue I ran into were the AA batteries, and it took me a while to sort out that they indeed the issue. The only 3 AA batteries I had in the drawer had been there for who knows how long and had apparently lost enough charge that they couldn't keep the system powered on. It would boot, then the screen would go fuzzy, fade in and out, go to lines, sometimes reboot. I started poking around Youtube, came across someone who mentioned that and after a new set of AA batteries it worked like a champ. The Retroflag Website indicated flickering screen was likely caused by the Pi/Connector board not lined up properly so i probably took it apart a half a dozen times before I figured out it couldn't be that and began to look elsewhere.
So fair warning on that, there does not seem to be any indicator beyond the system begins to lag then slowly die that your batteries are low which I'd assume can't be great for your SD card. Also with no external USB port if you're planning to use a Pi0 you will have to do all your config, rom transfer etc before assembly into the GPi-Case, I'm sure most know that but I'd say worth mentioning JiC.