I've been using a Griggs K-member and A-arms since '97 and really like the features that it offers (engine setback capability, lighter, revised geometry, etc.)... the only downfall to the Griggs unit that I can see compared to the other available today, is that some of the others (AJE and D&D come to mind) offer a bit more header clearance do to a slightly different design. I haven't read or heard anything negative/positive about the QA1 member, but I do use their adj. shocks and struts and absolutely love them, so they make some good stuff, IMHO.
You'll really like the advantages a tube K-member offer
The most difficult aspect I can think of installing one is using plumb bobs to square the k-member to the car... it was my first time ever using a "plumb bob" but I got everything within a 1/16" and the car goes straight as an aero, on a good track anyhow
I just took my time to measure once, measure again, and snug everything up, measure again (and again to be sure, lol) and rat-tat-tat 'em all down with the impact gun.
...and then head to the alignment shop.
Are you doing the coil-overs and tubular A-arms too?
If you've got any specific questions, let me know...
-Ryan