TQ as system gauge, and some comments to posts above
1. "Release of myoglobin" is essentially (not precisely) rhabdomyolysis in the case of total compartmentalization (i.e., nothing in or out). You also can release a shock of hypoperfused blood, clots, lactic acid, maybe reproducing microbes and their exotoxins, maybe a fat embolus, etc etc; however, "TK shock" is not going to be a factor for the vast, vast majority of urban and suburban incidents because your TK will NOT be on that long (if documented!). Crushing entrapments with prolonged extrication are another matter, but thankfully pretty darned rare.
2. Originally TK's were done because aid was so far off (WWII, Korean War away from landing zones). Later Korean War, and Viet Nam War, with transport times in hours thanks to heliciopters and shorter distance from FEBA to definitive aid, dictated that TK's were not necessary for many of the wounds they saw brought in because of the time element. Also many of the TK's were improvised, causing their own damage. Now that aid is moving even closer to battle injury sites (NO FEBA in assymetric fighting), TK's if they do not cause crushing or shearing damage are OK because they can be taken off in time. (Taliban et al answer that with shots to the crotch and head, but that's another story). Remember, however, this is MILITARY medicine, takes a few years to filter down.
3. Blanket rules are rules, but they are aimed at the lowest common denominator and the worst scenario. First-aiders need to apply TK when needed and leave it on because their "victim" will plead for its removal or loosening due to pain and fear; the victim will die if the TK is loosened, or removed, due to ex-sang. I think higher level practitioners need to balance time-to-help versus time to shock/death, but get the rules changed first, do the homework and cite it, don't just start making your own rules.
4. A good pressure dressing, backed up by a BP cuff say or done with a whole role of MEDIRIP (Coban), with a pressure pad over the proximal pressure point, will stop many bleeders...and co-incidentally stop all distal circulation....
5. A loose TK will occlude all returning veins including patent ones, causing most arterial inflow to cross-circ out the only outlet...the opened blood vessel and onto your ambulance floor...rather than some of it perfusing other parts of the limb and returning via the patent veins to the heart. (Hence the use of little TK's in phlebotomy). That TK has to be working 100%, or use the other measures.
TK or TQ is a systems gauge because it's use is based upon time ('til hospital versus exsanguination); is EMS close enough to definitve help, and is EMS still caught up in unflexible blanket rules, or able to accomodate higher levels of care and of the art of eval and tx?