Anyway, my unit is finally here, didn't bother to check the original fw, we know it's not worth the time. The flashing process went fine, though the final screen after the flash is done looks all messed up. Also note the actual linux flash command is sudo ./flash.sh (not sudo flash.sh).
A very quick review;
-shell format is nice
-buttons are ok
-screen is ok
-low performance, lower than the RetroMini, forget about fullspeed GBC or GBA
-no SNES emulation
-needs an extra tf card (increases the cost)
Final Verdict - while the custom firmware makes the use bearable, I really cannot recommend the device, unless you can get it for extremely cheap (think less than $25 shipping included), or you absolutely love the shell format (and can't afford a RG300). There is a chance the performance will improve with future fw releases, but still, remember the Powkiddy Q90 has the exact same price (about $30 on AliExpress), similar 2.8" IPS screen, and can do much, much more than the RG99.
But I have to admit the vibration function is hilarious - seeing the device almost jump off the table while getting flashed (vibration is always on during the boot mode) was amusing to behold.
Any chance someone could compile the SNES emu for the RG99? Would like to try Chrono Trigger, if nothing else.