For life-threatening extremity bleeding, a tourniquet applied correctly and immediately is the most likely way to save a life, at least according to CoTCCC. Medical professionals have many more tools and skills than I do and I won't second-guess them once they arrive; but as someone who isn't a medical professional I want to carry the tools and practice the skills that are most likely to solve problems.

The SWAT-T is better than nothing. Light, small, and inexpensive, it also takes two hands and significant effort to get full occlusion, and I've broken a few in training.

The CAT can be applied one-handed (for self-aid) and is easy to use correctly. Having trained quite a bit with both I made the space in my laptop bag to carry a CAT.

If you are not trained to use a tourniquet, go get trained.