Check out this link:
https://linustechtips.com/main/topic/480433-difference-between-rm750x-and-rm750i/
The RM750i has corsair link. That's the difference. Quality is the same. I'd stay away from it personally, I hear it's a tier 3 unit, and you're better off in the long run just spending the extra money on a better power supply. One good one I'd suggest is the Photon 750, it's also a tier 3 unit, but I consider it a tier 2, as I've never ran into a problem doing a high overclock on my 4790k. Right now it's 100 bucks, but if you wait, it'll probably drop to 90 or even 80 dollars, I got mine for 90.
EDIT: just price checked, you'd be stupid to buy either Corsair unit. The EVGA G2, a tier one unit, you can buy for 10 bucks less than the...