I haven't, but I didn't spend much time looking.
I did note that during the calibration using the ZIF socket, it detected a 0.02 Ohm difference between the highest and lowest resistance test points, which works out to ~10% of the ~0.20 Ohm average resistance detected. I haven't compare this to any of the ebay units I have (an EZM GM328, a Fish8840, and a 91Make "T4"). Nevermind, I misinterpreted and misremembered.
Any suggestions on how to better investigate?
I must say, this is my favorite of all the units. I like the rotary encoder, having a compact case, and the flexibility of test leads or socket. I think I may mod this further to allow in-system-programming without opening the case. The socketed AVR is less useful when I have to take out 3 sets of screws to swap it. Actually, the tedious part is mounting the board back in the case, since one has to slip standoffs under the board and keep them there until there is something to hold them in place. This fussyness could be remedied with some hot-glue, but I'd rather just have something I can access via the battery compartment.