I've spent the past couple of days testing my stash of NiMH AAs. It behaves pretty well if you load up cells with the tester off, then plug it in. Sometimes it doesn't always start right if you add cells with the tester on; maybe I need to tweak the state management code a bit. I have a bunch of cells that test around 90% or so of stated capacity, but there were others testing as low as 1/3 of capacity. :-|
The load resistors only get a little warm with NiMH, but they definitely get hot with Li-ion cells. At no more than 60% of rated wattage, though, they should be OK. Also, the tiny MOSFETs are doing their job without issue.