There is some good, some bad, and even some funny info on that link.....
About 90% of all Aftermarket gears (for the D30, D44, D60, and many others) are all from one importer that sells to most Every company whose name is on the box, and they just rebox. USA Standard have not been, Yukon 2nds or such, for many years. And actually are typically the same exact gears in box boxes.
I Sell mostly USA Standard as they are the least $, and same exact gear in the box as brand A,B,etc...As for a "warranty" well that bacially is a Joke on gears. If they are setup correctly then they wont fail, unless grossly over loaded, and that is extremely rare and typically not covered under a "warranty". Then the most common reason why a gear set needs to be replaced, is break in, no gears are covered under "warranty", against negligent/over heating of the gear oil, during the first initial 250-500miles. Or of course the last reason why a gear set needs to be replaced, improper setup, and not covered under a "warranty" either...
Now as to who to buy, I would HIGHLY recommend a USA standard or Yukon master kit. You will not find any others that have all the items they include. Ask if your master kit, comes with Inner axle seals for the front, or all the baffles, or all the slingers, or a HUGE assortment of set up shims? You have no idea how much easier it is if you are just slightly off on your setup and you want to just grab a .002" shim to add, or subtract. Rather than takes multiples and adding them up and then taking others and trying to produce that same amount with 3-5 other shim changes.
Spend Less, Get more, and get quality that will last you...
http://rwkhaussupply.com/usa-standard-xj-gear-package-special.html