Different fingering systems...
I started out on an Albert bass as a young tad, was switched over to a Boehm because (in the words of the teacher that I had for about a month) "we don't use that kind of horn here", transitioned to a full Boehm while in high school, learned saxophone and bassoon along the way, and finally scored a Oehler when I was an adult. While the different fingering systems can be a bother at times (last night at a pit orchestra rehearsal, I started "playing saxophone" on the soprano clarinet - rather bewildering when it happens, as you might imagine), none of them were beyond my feeble mind.
I have found that, when learning something new be it a computer program, a sport or a musical instrument, that it is best to do a little theoretical work (method book work, reading the manual, doing the drills) but also a lot of practical work. I find myself far more motivated to learn if I am accomplishing something at the same time.
Apple has issued a computer program called Pages that coexists quite nicely on the iPhone, the iPad and the Macintosh system computer. (There are some minor differences between the iOS and OS X, but in general they are the same program.) Now, I am a MS Word user on the Macintosh from about 1985 or so, and am quite comfortable with the program, but I can see the utility of an "all platforms" program like Pages. But, I hate to do the transition.
What I did was to take a piece of work that needed to be done (a five thousand word essay on a complicated game, complete with footnotes and references), forcibly put my beloved Word aside, and plunged in. No turning back, no giving up and going back to familiar ground.
For the first seven hundred words or so, I stumbled along, fumbling through the help files whenever I needed to master a procedure for footnoting or something. But, after that early threshold, it has generally been smooth sailing.
With the Mazzeo system, Rosario was enough of a realist to understand that clarinet systems often meet with resistance when introduced. The Ivan Muller "complicated" clarinet was fought tooth and nail by the music establishment when he proposed it. Even though the tone was superior to the old cross-fingered "simple" clarinet, the cries of "It's too complicated!" echoed through Europe.
The same was said of the Klose/Boehm, certainly of the Romero, and (I would imagine) of the "Oehler" horn. All the while, right there in front of them in the orchestra, sat the oboes, with their mass of interconnected key work, with complication upon complication. Go figure.
As a full Boehm player of some experience (almost five decades now), I have heard the "It's too complicated/It won't stay in regulation!" mantra for most of that time. I also occasionally get questions (being in a world of saxophone players who also have learned clarinet) about how to make some complicated set of transitions through the little finger keys that is puzzling them - I just point to the left hand Eb key and say "Get one of these..."
I have not put in the amount of time on the Mazzeo at this point to be able to agree or disagree with our Swiss friend's contention. I have only started fooling around with a working Mazzeo for, as mentioned above, every other friggin' time that I've tried to buy one (in pre-eBay and post-eBay days), what I was presented with was a stripped Mazzeo, where the former owner had taken Rosario's improvements out of engagement.
This summer, when the music season slows down (although it's hard to imagine it getting slower than it is at the moment), I'll put it on my limited practice rota (along with the bassoon - you can never spend too much time with a bassoon) and work my technique up.
However, I imagine that I will still pine for the missing Eb lever and articulated G#. For that matter, in one of the shows I am working right now (Hello, Dolly!), I am even getting some use out of the fork Eb. The last time that I did this show, I played the clarinet part on my Oehler horn, that due to the heavy use of sharp keys.
If a full Boehm one comes up somewhere, please let me know...