I still haven't flashed mine as I'm trying to find the original firmware just in case I want to go back to it, either MK-328 or GM328 Firmware.
The Chinese are not relenting to give up the original firmware and they usually lock the chips . Have you tried contacting the seller, maybe offer exchange for a positive feedback? In any case take pics of the "Menu" to see what they enabled so you can recreate later.
The most refined and reliable firmware is the "k". The automatic Capacitor test on pins 1 and 3 as great when you got a batch of caps to test. I think most testers are based on "k". On the other hand, the "m" is speedy, flashy, with extra features but might need some tweaking.
Above statement is my opinion.
Mine is based on 1.12k firmware, but I do like the Font, Layout of symbols and readability, I think it's been tweaked slightly.
I'd love to see some screen shots of M firmware but cannot find any anywhere.
I took some pictures of mine, testing a few items and also the "Hidden Menu"
http://imgur.com/a/xWu9n
I used this one (trendy 1.22m) and it seems to work.
https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg964239/?topicseen#msg964239
I can't compile with the config.h and Makefile from that one because the layout for the files has changed between 1.22 -> 1.24.
I can only power my device using the usbasp at 5V (need to buy some 9v batteries, hehe) and I only have 3.3, 5 or 12 volt power at home for the moment.
The text is good with the 1.22m but I can't post pictures using it because the unit does not like 4.5V - 5V from the usbasp. Getting some text and then "Bye!" because of low battery.
I know it is possible to make it accept 5V or lower if tweaking the Makefile or config.h but I don't know how really and as I said, cant use the config.h or Makefile for 1.24m.
Could someone please "port" the linked files to compile on 1.24m for my tester? I have found different Makefiles but I can't say I know what I am doing. One Makefile made it work but the text on screen was inverted and in the wrong position (at the bottom) and then I gave up.
Edit: I also have the LCD TFT-color unit you talk about above and I'm NOT messing with it.