I highly recommend the SOF-T. Only one I had personal experience with, putting it on another person. Easy to apply, secure. It can be applied with one hand, which is important. You can tell if it's real, they're strong as hell.
Rule of thumb, if shooting/squirting blood, severed major vein/artery or significant limb mangling, use a tourniquet. Get to a hospital immediately. Or EMTs. Longer time goes on, more likely of damage. 4 is the shortest time for losing limb, but routinely many times that. 8 is more common. Generally you really don't want to loosen up a tourniquet after applying it. It is/can be done, but by medical folks, not any of us.
Apply at least two, three inches above wound (ie towards torso). Below the elbow or knee is better than above it when possible.