I just took the Serum ones for a spin and have to say they sound pretty good in general, though there is a bit of "sameness" to them..think it's the SAW sound in most of them. I get that Serum has a pretty individual sound and it might be hard to turn out something different, but a few more Sine-based pads would have been nice.
Personally, being into ambient music, I wouldn't have much use for these in their current state/form..but that's not a negative thing at all..just that they're not really suited to my kind of music I guess.
All that said, I'm sure there are plenty of peeps on here who will just love em.
Good luck with selling them..hope it works out for you.