I used to have long hair, it was a pain in the ass, hard to keep clean and I don't miss it. I'm sure some folks will find out that it's just a lot easier to have short hair, but I do appreciate having the option (at least in the winter). Similarly facial hair is okay in the winter, but drives me nuts when it gets warm out, but will like having the option to have a goatee and/or sideburns.
Some people will go nuts, most won't really care one way or the other, and if someone has a bit of fun dyeing their hair or messing around with their style who cares? It's still pretty easy to keep things neat and tidy and look professional if you just do some proper grooming.
Facial tattoos are still job limiting though, so hopefully people give that a bit of thought ahead of time if they ever want to get a job outside the military, but really that is a personal problem.
My only concern is that people that should know better will leave it up to lower level units to figure out he 'operational requirements' bit instead of giving clear direction, and folks will get hurt as a result. For the Navy, should be pretty straightforward that if you are on a ship not in the dock and you may be responding to a fire, you need to be clean shaven, but from firsthand experience a lot of people will play silly games and try and Philadelphia lawyer their way around it. The folks at the working level that get dragged into it have way too much to do as it is, so it will waste a lot of people's time if there isn't some kind of NAVFORGEN to clarify things.
@KevinB that doesn't work when you start moving around and sweating; the testing we did was both at rest, and then working (I think on a treadmill) to see what happens when you are moving around and sweating. If it gets hot enough to start releasing flammable vapours things have gone wrong anyway, but that's something to pass a check in the box instead of a safe option in the real thing.
Lot of variability by people's face shape, hair coarseness, facial hair density, length etc but no one managed to keep a seal when working in SCBA after a few days growth. Some were okay on the at rest test, but everyone failed the working portion, which is where you'd actually be exposed to the toxic fire gases (which can be superheated).
People that lose a seal will run out of air fast. At best, you retreat to a safe area, which means that whatever you were tasked to do with is delayed and someone else has to do it. Maybe that means a fire burns longer, gets bigger, and puts everyone at risk. Worse case, you become a casualty in the space, your wingers try and get you out, and whatever you were tasked to do is still not happening. Ships are tight quarters, with small openings, nearly vertical stairs and no good way to get someone out, so you put both yourselves, your winger, and everyone else at risk. Unless someone comes up with some kind of hood that seals somewhere other than the jawline, requiring shaving as an operational requirement for anyone that needs an SCBA is really a no-brainer.