I've never used one, and I don't think I've even ever seen one in person, but as far as I know, they're alright. Not the best out there, but not the worst either. Some SDS stuff is of questionable quality, but I've not heard anything specifically bad about the RACK.
Unless you've got a lead on a good deal, I believe it isn't very well priced compared to similar aftermarket options. Opinions will vary, of course, but I believe that something like a Tactical Tailor MAV would be a much better deal and will hold its value better, too.
As far as the specific pouches designed with the the RACK, I don't really like them. The dual M4 mag pouches with the shotgun shell loops on the front (Which I have seen and messed around with) are sorta goofy and I think better can be had for the same price range.
I'm not really familiar with any of the other pouches that were included in the RACK package.
The RACK platform itself will accept any PALS/MOLLE compatible (Tactical Tailor, Paraclete, Blackhawk, etc...) and if you rig it up right, many LC-2 (stuff that uses ALICE clips) can be made to work with PALS webbing.
Mainly - Unless you're fine with a replica or have a good deal on a used SDS one, I'd skip the real one in favor of something else like the aforementioned MAV.
However, like I said, I've never seen or used one, so find another source of information too.
