I wear the Traditional mask. I am not a fan of the HSM. I've tried out a couple and I just don't like them. Of course if you are of a certain age (older) and were a catcher, your experience with the HSM can be limited.....it wasn't an option when I played for catchers or umpires.....
But I have tried it, a good friend loaned me his one summer when he had to take off umpiring due to some health issues......I never developed a liking to it.......I found it hot, restricting and awkward. My calls seemed to reverberate inside it and I could never find a good way to manage it when it needed to come off.....the little things I needed to "hear" seemed more difficult. (I'll agree that a HSM mask gives you more side and top protection.)
I always thought that as the HSM became more common/required in the youth/HS leagues that the traditional mask would lose its popularity as the youth moved up to college/pros and then also on to umpiring, but I don't see that happening. I see many catchers ditching the HSM for the traditional mask and helmet.
In my HS games, it is not uncommon for HS catchers to try and use the separate mask and helmet that they have been using in travel ball for a NFHS game. They usually have the approved helmet in their bag and grumble when told to change.
My own son who caught in college, ditched the HSM for the traditional mask/helmet even though both were provided to him. Its personal preference....... in my current association, I would wager that its 95% traditional 5% HSM
(And yes there are still no definitive stats or science to prove or disprove which is safest. Some even say the HSM transfers more force to the head and neck versus the Traditional mask.)