I'm looking forward to the 5x5 a lot, and maybe their 6x6 will be good enough to make me interested in 6x6. Right now, I don't practice it because Shengshou 6x6 is so awful. Moyu's can't be worse. I don't see myself getting the 7x7, though. It's pillowed, it's bigger then the Shengshou, which is something I don't like about it since the Shengshou mini 7x7 is the perfect size, and it's expensive.
Hmm... thinking about this again, perhaps it being pillowed will make it feel smaller and easier to hold. I have heard that about pillowed cubes. However, I've never tried a pillowed cube, and it didn't immediately occur to me that it would erase the feeling of a 7mm size differential from the mini Shengshou to the Moyu.