You are right, is simply a Snell hook tied over a wire. Fishing in fresh water I could probably cast a shrimp forever and not lose it unless I set the hook or get a good bite. Fishing salt water it keeps the shrimp on long enough so you can hook a fish before it rips off the shrimp. I don't use this hook in fresh water but maybe I should try it. I use it for ocean fishing for perch, sea bass and kelp green ling.
Sorry about the terrible pic, it took me over 30 different tries to get that one. I suck at taking pics up close. Will see if I can get the other hook to turn out better. Is a bronze hook so maybe it will show it better.
I think this picture shows it better.
You can either make it that long so that oyu can wrap the bait or make it shorter so you just take it over the bait and wrap it around the shank, either one works. I have caught 3 kelp greenling on the same shrimp since starting to use them.