Below it's a copy-paste from Bill's story I was impressed by: shows me that we european spearos have a lot to learn from americans. Slip tip, co2 cylinders, the spare float on your belt are all things that we don't use over here. I can tell that most of my buddies, friends and clubmates have never heard about those things.
The float use may be more specific to our thick kelp, and not all that useful to you guys in the Med, but I have had a lot of use for it here.
Our white sea bass go wrap the line up in the kelp, often in poor visibility. We have to dive down and cut kelp to bring the fish up, and often its quite involved and laborious. If a fish is at my depth limit, its very difficult to be working down there, severely negatively buoyant in a thick wetsuit. The float I use has two 16 gram CO2 cartridges so that it can inflate at depth, and a vent valve that lets the expanding excess gas escape as it ascends.
Often I can brain the fish, detach the shooting line from the reel line or float line, attach the float to the slip cable, pull both toggles, and the float will pull the shooting line out of the kelp and bring the fish to the surface. If it doesn't quite pull the shooting line through, at least it pulls the fish up until it brings the line taut, and then I can see what kelp needs to be cut to free the fish.
Of course it has other uses as mentioned in that story. I can inflate it and attach it to the gun to make it easy to find in the kelp. I can attach it to the reel line or float line to keep upward force on the line while I go down to see what is going on. And as mentioned in that story, after I get the fish up, I can attach it to the slip tip cable to float the fish at the surface while I go find my gun and reel all the line back onto the reel.
I guess I should say that its not universally used here in California, but it seem to be catching on, particularly among guys who have dived from my boat and seen it.
I like this thing so much that I should be on commission, but unfortunately I'm not.