The EMS light is a specialty light.
It's useful to light up stuff in general. Yet to the discering hobbyist the beam seems...well, ameture-ish.
Streamlight designed it to have 3 distint amounts of light from the same emitter.
Say you're observing a football player who got his bell rung. The center beam on low is designed to cause distinct pupil reaction while the second ring throws subdued light to the other eye while being dim enough to not cause pupil reaction. There is a purposeful shadow between
^^ note the shadow and subdue'd beam next.
This allows the EMS tech to compare when checking for a concusion...
The offset emitter is part of the magic. Once one gets accustomed they rotate the light one way or the other to tweak the lighting based on persons head size...little kids faces have far less gap between the eyeballs than say...a 6'5" pro athelete.
^^ note the shadow causing ring around the emitter.
^^ no ring in other lights.
I am not an EMS tech, but I studied this particular light before buying it. It's a niche light.
I have kids who play sandlot football, ride skateboards etc and occasionaly get their bell rung. I've watched EMS folks use pen lights and figured what-thuh-heck, add it to the collection...
Regarding the circuit disruption, a dab of pipe thread tape or plumbers putty will cause the tail cap to stay put. Perhaps a 'fatter' o-ring...
I just cinch mine down nice n tight and it stays put.
Or it can be used like a tac switch.
I do that with my TL 2 LED light sometimes.
Maybe one day I'll contact a propeller head at Streamlight and enquire why some lights become inoperative when the cap is loosened while others do not.
Sometimes ya just gotta crawl into the mind of an engineer and ask "what were you thinking man?"
That's one of the main reason I dig the modern flashlight and focus many times on niche lights.
Too many companies focus on MORE MORE MORE these days. More light, more bright, more power!!! But it's what sells, so why not right?
Even Streamlight plays that game with some lights. Afterall, they were the first to build a light that exceeded a million candle power by building a 5 million candle power light for NASA in the 1970's!!!
These days they also play the game of niche lighting and have been rewarded by selling millions of specialty flashlights to folks who have a particular need where peoples lives are at stake.