Erik: I believe that LEAF's aluminum U-brackets were/are used in the Air Command series gyros -- in places quite equivalent to the similar Gyrobee: trailing links, vertical struts.
I've never known of one breaking on an A.C., and some of them took a fierce load just from the misalignment that was originally built into that design.
U-brackets are actually a fairly awful way to connect tubes together from the structural viewpoint. A U-bracket forces the loads off-center compared to the bolts at the base of the U. This in effect wastes much of the strength of the tubular strut that's bolted to the U.
But they were very widely used in hang-glider-based ultralight planes, and the early designers of ultralight gyros took over the practice from Quicksilver, Teratorn, Drifter et al. They are easy, cheap and fast to install. You just have to beef up the joint to compensate for its inefficiency.
Getting back to cluster plates for a sec, my copy of the Bensen material specs called out 5051-H32 for cluster plates and all other plates on the gyro. This alloy polishes beautifully and holds a shine, but it's much softer than the 6061-T6 of the tubes. But Bensen's plates were massive. The Gyrobee's cluster plates, in contrast, are just 2" wide strips. Moreover, the 3/16" bolts have a smaller bearing area inside their holes than Bensen's 1/4" bolts. I suspect that's why Martin Hollmann specified steel instead of 1/8" aluminum for the 'Bee cluster plates.