I was an EMT 25 years ago. Back then, tourniquets were a final option for arterial bleeding. They were discouraged. You had to loosen it every few minutes to prevent the limb from dying. At some point in the past 25 years, likely due to battlefield wound care in Iraq and Afghanistan, someone realized that stopping the blood flow is the most important thing. Tourniquets are crucial for stopping arterial blood loss in limbs. If you don't stop the bleeding, the patient will die before they get to the hospital.
Yesterday I mentioned and linked to the three main types of tourniquets on the market today. Here are some videos on their use so that you can compare and find the one that fits your needs best. All of them work. They each do different things better or easier than the others.
SWAT T Tourniquet
Of course, clotting gauze is also a huge improvement to bleeding control over the past 10-15 years. Quick Clot gauze is an amazing product. Something to keep in mind is that you don't use it to stack on top of a wound or wrap around it. You take your finger and shove the QC gauze down in the wound. Pack it in there deep and tight. Then apply 5-10 lbs of pressure to it for five minutes. Do not remove the gauze - let the ER docs do that.