+1 on functionality and reliability. With that price it's usability must be good/very good, and it must work consistently and reliably. That should be the main focus. Throw out customizability and easy modifiability if they get in the way of reaching functionality and reliability.

I might pay 150€ for it if it really is functional and reliable. If it's price was 100€, I wouldn't demand as much functionality, but I still wouldn't spend even that much money if it wasn't reliable at least.

Just my two cents.

PS: don't still make it look like a frankenkbd : P