Each of the amps compared here have unique features that deserve attention. Further information can be found at:
Flex PowerGenius XL
RF Kit RF-2K+ and the YahooGroup (manual, photos, etc)
SPE Expert 1.3K-FA
I'm happy to see a kit being offered in the QRO category - long overdue IMO. I've long thought that a KW tube amp would have made for a popular commercial kit but now that technology is moving from glass to MOSFETs, I hope the RF2k+ does well.