Having owned this keyboard for about a week, I can say that my first impressions higher than expected. I didn't expect to be blown away by a keyboard, but the sleek design and typing comfort is extremely satisfying.
On receiving my first K750R (not from MA), one of the shift keys was a little disjointed, and a couple of other keys made loud ‘clack’ sounds when pushed, though the one I received as a replacement has no such issues.
Layout of keys is spacious and logical, and the solar-powered function is extremely efficient and useful. Even charges when it's switched off!
One small gripe I do have is the fact that the caps lock, num lock and scroll lock buttons do not have dedicated lights on the keyboard to tell you whether they're on or off; instead, pushing one causes a notification bubble to pop up on-screen notifying you of the change. Not a major concern, though can be slightly annoying when the programme you are running sits atop the notification bubble, meaning you can't see it.
Overall, a great buy! If it broke tomorrow (and I didn't have a warranty), I'd buy another without thinking.