I have used a Trango Cinch for a positioning lanyard, in both the New Tribe/Chameleon combo as well as the Sherrill/Beeline kit. I have not had any problems at all, and I must say I love the Trango Cinch.
Before the Trango Cinch I used a Hitchclimber on my lanyard as a slack tender with an eye-to-eye beeline prusik. The only benefit the Hitchlimber gave over the Trango was that it allowed a single attachment point to my harness, as the lanyard could clip back into one of the carabiner holes on the Hitchclimber. The Trango requires two connection points, one for the cinch device and a second for the standing end of lanyard.
Here is a pic of my rig, with my main climbing line (Poison Ivy) using Hitchclimber, and my lanyard with the New Tribe Chameleon rope and the green Trango Cinch.
The main advantage the New Tribe kit has over the Sherrill kit is that the NT kit allows for (and comes with) a friction sleeve, a scaled down 18" version of their Dan House Rope Sleeve. The Sherrill beeline rope is lighter and throws a little better, but since they put spliced eyes on both ends, you can't use a rope sleeve (unless you cut the stopper eye off, and use a knot instead).
All in all, the Trango Cinch is fantastic, functional, and wonderfully simplistic in its design. I haven't experienced any jamming whatsoever, and it lowers me just fine from my lanyard TIP..always smooth as butter and in a very controlled fashion.