I did a number of shorter climbs, 25' or so, before I took it out to the woods last week. Then I did two 75' climbs, one after the other. A couple of things come to mind about the hitch. I'm using the 8mm Beeline that came with it, which seems quite satisfactory so far. The first stopper knot is tied to the dogbone, and left in place. After a while it gets as tight as it possibly can. The second stopper knot is tied each time the hitch is applied to the line, and the trick is to get it to cinch up as tight as possible, which means tying that hitch so tight it'll barely move up the line at first. After working it a bit, it seems to find a sweet spot, but that takes some time. That dogbone mod is a very smart idea, and it looks like it could be a real improvement to this system!
I found that as I was climbing, the HH was in a slack position much of the time, as my weight was alternately on the upper and the lower ascender. So before sitting back to take a rest, I made a point of tending it up by hand. You're right about that, you need to keep an eye on it! In descent, the hitch was very responsive to pressure, from light to moderate to hard with corresponding speed. On letting go, it grabbed instantly.
The energy efficiency of an SRT ropewalker system is impressive, and I'm looking forward to learning about the work positioning potential of this style of climbing. However, I see that the mindfulness factor is high!
I appreciate your input on this AJ, and I'll be reporting back as I explore this further.