I've got K760 (Mac one) and it's simply amazing. I think it's died on me once (when it didn't get enough indoor lighting) in like 1.5 years.
I tried the K750 and found the keys spaced out wider than I was used to. Did you get used to it?
I switch between a Macbook Pro and a Windows ultrabook (long story) and the keys are spaced slightly different on both. After couple days of finger-confusion, my hands just adjust to them easily. The mind/body is amazing that way.
I've been using this K750 with the solar panels for a while now... no issues whatsoever.