To answer you original question, I tried a set of Briley sidekicks in 28 ga. I did not like the way they worked. Half the time, the extractor pulls the unit(s) out of the barrel, because they're only held in by friction by a small nylon disc. Then you have to manually extract the spent hull from the device, re-insert it/them in the chamber before you can reload. Patterns were spotty, and picking up a few spent wads will show why. Gas blowby destroys the base seal.
Companion tubes are probably a better choice, but more expensive and add more weight.