Think of this as giving your car leadergear type (or very close to it) final drive ratios for 2nd-4th gears then 5th is your old "real" 4th gear and 6th is your old 5th gear. The advantages of leader gears (in gears 2-4) without the drawbacks!
If the answers to my questions below end up favorable and he is able to implement my carbon disc/carbon fiber DS suggestions at a comparable price point this looks like a really neat option for those considering a complete drivetrain upgrade.