The BladeForums.com 2024 Traditional Knife is available! Price is $250 ea (shipped within CONUS).
Order here: https://www.bladeforums.com/help/2024-traditional/
It uses the tip of your thumb. Put just the tip of your thumb nail in the spyder hole (need to word that carefully) and flick your thumb straight out, in line with the knife handle, not away from handle (perpendicular). To shoot a marble you also dig your thumb tip into your index finger so you can put pressure on your thumb and then release to get a better flick. You can do similar by putting ring finger and/or pinky on the tip of the blade and applying pressure with thumb. Then release the blade and flick which will give a harder flick. Its good to also learn how to hold onto the handle or clip with the tip of your fingers so you don't throw the knife out of your grip. Also depends on the knife how easy this is. The Para 2 works pretty good. Also works good on a lot of thumb stud knives.