I cant comment on the LF Hifi X as i havent tried,
Though i am currently riding the 2013 Airush Razor.
I have been riding the Razors for the past 3-4 months, and after that i dont think i could ever go back to a delta

The relaunch is a breeze with the 5th line, you just need to know how to use it. At 55kg i ride my 7m in 20+ knots, and at around 25knots its boosting time, it really does rip you off the water and take you up if you send it hard. It likes to be ridden with the bar pretty far in most of the time, which i like, and unhooking is clearly what this kite is designed for. Compared to the fuel i found the Razor had a bit less bar pressure and got better slack in the lines when unhooking to pass the bar, for that reason and because the razor has the 5th line, i prefer the Razor. I found the Razor took a few session to get it dialed and get comfortable with it, but once that happened i haven't looked back

If you do go the Razor you will be stoked, i couldn't be happier with mine, it also comes in the Team version, with Kevlar reinforcements to stop the canopy from stretching over a few years of thrashing.
(Disclaimer: YES i am a Airush team rider, though i would still be riding this kite regardless of the sponsorship)