Anyhow, I tested it out, and it worked very well!
It didn't quite work as well on shrimp for me, however, even though it was a "shrimp" sheller... I guess the shrimp I had were too small for me to fully utilize the sheller. I used it on shelling crab legs and I could very easily pick the meat up with a fork afterwards.
So I have the shrimp sheller in my bag (almost) all the time now. (!) You never know when you need to shell a shrimp or a crab leg, or any shellfish.