Legal or not, I DO NOT reccomend this clone. It is similar and compatible to some extend but it lacks features like an EEPROM. With fuses you can only reserve some FLASH to emulate an EEPROM. Thus have less space for your code.
Also the manual is only available in chinese. There are english translations but those are hard to read as the layout got screwed up....
As legal as any other clone CPU / MCU. See
Intel vs The World
In short: if you copy the silicon design it's illegal. If you create it yourself from the ground up it's legal.
However, IANAL, so don't quote me on that.