The spider diff is worthwhile.
The fancy alloy purple bits are a waste of money, and the quad brakesi dont know about, but my two discs work fine, and if you are having problems with the brakes buying craddock discs would be a much better and cheaper thing to do. So buying that package i would say no . If you want a spider diff, i bought one off eBay for about £25 i think, although i only bought it because my old one stripped. And they come with nasty grease inside, which shouold be replaced by oil.
mike