Here is my experience with both bismuth (Bi-Sn alloy) and Kent TM.
When pattern testing Bi-Sn I always found a few hole in the paper from fragments of a pellet. This appeared to be only a few fragmented pellets, perhaps only 1-3. Otherwise, all the pellets were accounted for.
Have killed at least 100++ ducks with Bi-Sn, mostly over decoys and do sometimes find fragmented pellets. Much more often, I get deep penetration, sometimes totally through even large mallards at 30-35 yards. Loads were 3/4 to 1 1/4 oz of #6, #5 and #4 at 1200-1250 fps.
I used TM #5 together with Bi-Sn for two years. Also excellent performance on ducks. About the only practical difference was that TM seemed to respond more to different degrees of choke in the two guns I used it in. Bi-Sn consistantly patterns 80+% in nominal (actual constriction) full choked barrels and high 70s from 1/2 choked barrels in my 12 and 16 gauge doubles.
Niklas
