I'm not 100% positive, but I think EM just designates EastMall. I have a Riva set from Liberty Flights, no etching but they're 901s, that has what I believe to be the original booklet with it. It says "Hello-UNC & Riva & Mega Riva" on the front, and IIRC the original Riva was made by the same company as the Hellos, which would make this set genuine.
I also have a set that has Riva etched into them, 1100 mah though originally they were advertised as 1300, that came from Eastmall. There was no booklet with them, the presentation box is different, and I hate to say it but the quality is not on par with the set I got from Liberty Flights.
Needless to say, there are so many different companies in China knocking off other companies' product that it's really hard to tell which ones are good and which aren't. Heck, Rivas were originally knock offs of the eGos, they just happened to have gotten them right.
I also have a set that has Riva etched into them, 1100 mah though originally they were advertised as 1300, that came from Eastmall. There was no booklet with them, the presentation box is different, and I hate to say it but the quality is not on par with the set I got from Liberty Flights.
Needless to say, there are so many different companies in China knocking off other companies' product that it's really hard to tell which ones are good and which aren't. Heck, Rivas were originally knock offs of the eGos, they just happened to have gotten them right.