Who knows how compatible it is. There don't appear to be any makers listed on the boards silkscreens (or they positioned the boards so you can't see the maker marks which is common on these 'compatible' boards). Maybe it is 100% compatible, maybe not.
I will note, they mention USB cable X1, which might mean they use the older UNO method of downloading firmware with the FTDI cables, and not the method used in the R3. I also see a note that you may need to take off the ethernet shield when downloading your software. If so, taking the shield off and putting it back on would be a hassle during development.
Obviously, the Arduino team gets no revenue from this sale, if that is important to you.