I have tried a variety of bobber stops and always go back to the Thill string version.
Tips and trick's on the string versions.
Always leave about 3/8" tag line at each end and clip the rest. Aids in tightening the stop if it comes loose. Mine typically come loose after a few trips out. More time than not I break off before the bobber stop, stop's working. When I break off, I tie on a new bobber stop. As for cinching it down, wet it with spit, pull the tag ends and clip off the excess leaving 3/8" tag line.
You are using a spinning rod correct?