There are a couple of very similar boards I've seen around, most are based in CH340G serial adapters (more durable/reliable that the 16u2 used on official boards, but without the special features of that which hardly anyone uses). Robotdyn is one if the better chinese elecronic crap companies.
Those boards work fine unless you're doing something wierd that requires reprogramming the 16u2 to make it appear as some other USB device.
All an Arduino is is a microcontroller, a USB port, and a serial adapter (or for pro mini, just the 6-pin header), plus a linear regulator (ranging from "decorative" to "passable" in terms of current handling), connected together in the obvious way,and every other pin of the microcontroller brought out to header, and ideally with any needed bootloader preloaded onto the chip.
Personally I wouldn't use an atmega2560 for anything if I could avoid it (they had to make a couple of compromises that are kinda ugly to get that many pins, and break the 128k flash barrier, they cost a fortune even as bare chip despite being like a decade+ old.... You need pins, or flash? (generally, you want a part with not more than 128k of flash (at which point it needs a third byte for the program counter), unless you really need the flash, and not so many pins that they can't fit the pin registers in the low I/O space (Not surethe boundary on pre-2016 parts, on the modern ones it's 56, which is exactly reached by the highest-pincount devices available on the modern avr architecture._