Full disclosure, I have both ShineMate and Rupes battery powered machines, so I'm not necessarily biased with the following comments...........................
Prior to the ShineMate's, only Flex was offering decent battery powered polishers. Back then, in Australia the battery Flex's were astronomically overpriced. Put it this way, I could (and did) buy a 3- and 5-inch machine, with 4 batteries, a dual port charger and a carry bag for LESS than a one single Flex with 2 batteries and charger, no bag or case. So, they were supremely competitive in pricing, and actually, they have put Flex on notice because the prices on those have come down in recent years.
When the ShineMate's were launched, the machines were all new, not a corded polisher with the cord cut off. The newer EB210 takes the PXE-80 concept and takes it to another level, especially the battery design and placement. On the 18v system, the chargers are sequential and have cooling fans to make charging more efficient without causing overheating issues, fairly sure the Rupes equivalent doesn't have cooling. So, while they may appear as a Chinese knock off brand, they are actually innovating and making things better. Meanwhile, Flex and Rupes sat on their hands.
To back all that up, from what I was told a couple of weeks ago, the ShineMate's are apparently very well regarded among the professional sector. In particular, they offer more torque and superior rotation, in fact, the one machine that was singled out was the Flex, that they stall too much. The other highlight was durability and reliability, which is something that wouldn't go unnoticed in such a high-use environment. Put it this way, the fancy Italian brand is not well regarded for reliability, which is disappointing to hear when the tools sit at a very premium price point.