I utilize a Griggs K-member and tubular A-arms and QA1 coil-overs(at the time of purchase D&D was the only other manufacturer of a tube k-member, now the market is flooded with choices)
As far as the revised geometry goes, the k-member sets the tires forward and out for a longer wheel base and wider track width for high speed stability and better weight transfer depending on what you use it for (I drag race). The obvious difference is going to be weight savings. You also have the option of setting the motor back 1" like I did... you have to shorten the driveshaft and possibly modify your x-member depending on your tranny setup.
More header clearance (AJE is claimed to have the most, I believe) and easier access to the starter is also a plus. It just makes everything "cleaner" underneath
As far as installation, you have to get some plumb-bobs and square the k-member with the rear end, which the directions with the griggs unit are pretty thorough... IMHO.
Good luck with your choice for a k-member... the griggs is a nice piece, but the AJE is what all the drag racers rant/rave about. I've had my griggs k-member since '97 and the only complaint I have is that it puts the tires really close to the front/lower part of the fender well... I had to do some cutting to get the 17'' Konig villans I ran a couple years ago until making it an all-out drag car, the skinnies clear nicely
Hope this helps...
edited to add: the griggs k-member comes powder coated gray, others come powder coated black
