The one I originally posted works by sandwiching 4 plates together with one screw/lever, one side of plates has teeth to hold the boom at your angle and the overside has "C" shaped cut outs to hold the arm (sliding it in and out to find the ruff balance point)..... all with one lever, so first its a royal pain adjusting the angle because you have to adjust it over the teeth, its hard to move then all the sudden free falls to the next tooth with a cluck and bounce action, worse than that to get move it has to be really loose so your arm pivots in the "C" cutout and want to slide downward.
This one is the other Ebay version I see (happens to be from Amvona when they where on Ebay) I got it for around $100 with shipping but I added casters and a fairly heavy weight to the lowest center column section (probably a good idea for any sub $500 boom)
It has separate controls to slide the arm up and down along the fulcrum and also lets you twist the arm to change the angle of the light without climbing up to the strobe (first pic top screw knob) adjusting the angle is exact, no teeth to move over... just loosen the large handle tilt and re-tighten (second pic larger handle/knob). This one gets used about once or twice a week for over a year and so far no issues for what it is (a fairly safe low cost solution)
I really cant say anything about the Bogen/Manfrotto version in the B&H link other than to say it looks to much like the teeth version for me to try.