I have never used their kit but it appears they don't have a parking brake provision hence why they are so cheap.
Nothing wrong with that but I wouldn't want a street car without a parking/e-brake!
I myself used the SSBC kit on my 8.75 rear and it was pretty easy to do and seems fairly high quality. It will set you back around $600 or so though...
Also make sure you change out your factory proportioning valve under the master cylinder to bias the rear brakes less or the rear will tend to lock up too easily. You can use an adjustable one they provide you but I went with the GM style unit from inlinetube.com which is biased properly for a 4 wheel disc setup!
Good Luck!