I have the M2 Pro version and while I can say that it sounds great, it isn't without flaws.
No1, UI looks like a MP3 player from early 2000's. No album art, etc. On the bright side, it is snappy and responsive.
No.2 Since the DAP runs an Class-A amp, it will run hot and battery life will be short. It's just how Class-A amps are.
No.3 Output power is on the low side. You might need a separate amp when using power hungry headphones like planars.
No.4 No USB DAC support. Won't connect to your PC, won't connect to your Mojo.
No.5 No WiFi, no Bluetooth, no digital output.
As for microSD compatibility, I've tried 64GB and 128GB cards, and as long as you format them to FAT32 they were usable.
I would not recommend this to people looking for their first DAP, there are plenty of DAPs these days that can do a lot more at or below this price. If you have a daily driver DAP, have some extra cash to spare, and want something "unusual", this might be for you.