I think the sling is the tool to use. The barbed paralyzer tip is very good at holding the fish. For practice get to a shallow area on the sand and shoot at small chunks of dead coral in the sandy bottom. You will learn to figure out the refracted angle to hit the spot or target. Also you will start to learn to breath while shooting. All too many times have I seen shooters hold their breath while aiming. Wrong thing to do, as usual, underwater we never hold our breath for any function we are performing.
Lion fish pretty much are like shooting ducks in a barrel except the difference is the new angle you cant see, just imagine. They are very secure in their ability to hurt you if you touch them so they dont move much. Only if they have been shot at before will they move usually.
Also hunters should carry surgical scissors to cut the fins off the lion fish. Find out which ones(fins) will sting. Also the reason for practice is so the coral that is usually behind the fish wont get hit. Another thing if one is sitting in a barrel sponge, please move the fish out of it. Just be careful not to harm the coral. Take your time. It's better to get one in a dive and save the coral than to get three and kill coral also.
I so look forward to hunting with you guys. The barbeque part is the best. kevin