The replica tourniquet is obviously just a bit of dress up kit, if someone's got an arterial bleed then using a replica on them is probably better than nothing... but still not really appropriate, belt or sling would be better
Current doctrine is 2" above the wound, or above the joint if there's one in between. If you can't tell where the wound is, or the trauma is so significant the artery could be smashed up inside, go to the base of the limb, couple of inches below the groin or armpit (though this will be less effective at stopping the bleeding and carries greater risk of unnecessary damage to the limb). Fit the tourniquet, wind on the windlass til the patient stops leaking and mark it with the time of application. Haemostatic agents then get deployed en masse to to block up any residual bleed since even the tightest tourniquet isn't going to be 100% effective.
That said, if you're applying a CAT to someone at an airsoft game then shit has hit the fan MASSIVELY and that person is lucky you had one on you!