I tried both the Buckingham throttle and the ART blackbird at the treecare show in Germany last week. Not real climbing of course, just a few meters up and down the rope, some lateral movement etc.
Throttle seems to hold on the rope super hard and it took a lot of effort to disengage. Not smooth at all. I've been told that it gets better once it's a bit worn-in, but out of the box it didn't feel very good.
The blackbird is relatively chunky, but it felt super nice to work. Smooth ascent and descent, easy on and off the rope, easy switch between SRT and DRT. Was quite fun to use. No idea of course how well it handles things like sap, wet ropes, etc. The tending pulley also looks rather small, so I don't know if it tends as easily as a RRP or a Zig Zag.
