I was given a large can of Sera sturgeon pellets by a fellow whose wife bought it accidentally, thinking it was for pond goldfish. I used it as a component of my DIY gel food mix, but I would never actually buy the stuff on purpose. It was high protein, but aside from fish meal, the first several ingredients were all wheat. I recall that it was something like 3x the fat content of Massivore pellets.
On top of that, the pellets were ridiculously small for catfish, although their small size made them easy to incorporate into the gel mix. My wife joked that my gel foods without and with sturgeon pellets were "smooth" and "crunchy" versions.
I think they are a cheap food with cheap ingredients, sold cheaply to folks who keep giant fish with giant appetites.