I got my Yankee Hill Tube kit today...I got the Customizable one, in the "specter" length. It's an Armalite upper, with a 16" Oly match barrel...not the SUM, just the plain match.
The kit comes with the tube, a 12" rail, lo profile gas block, sling swivel, sling stud, the end cap for the tube, and the flip up front sight. I ordered an additional 3" rail for the bipod on the bottom. Interestingly, the two holes towards the front for the sling stud are at 4:30 and 7:30...you can't seem 'em in these pics.
The tube seem pretty sturdy, but it's not really thick...and it feels lighter than some other tubes I've seen. I forgot to weigh it before I put it on, so I don't know exactly what it tips the scale at.
All things considered, it's pretty cool....makes for a different look, and I like the look of the end cap.
I think Yankee Hill has done a good job with the stuff I've gotten from them so far...good quality, at prices most of us can afford.
BTW, the kit was $235...but you can get the quadrail type w/o all the shizzle I got for about $120...and I think they sell the lightweight one even cheaper than that.