. . .it's a lovely watch, and the fact is that it's really value added to be able to ogle the works through the caseback. I think functionally the nylon brake actually slightly has the edge on the metal one (of course, I have no authoritative evidence of that, just an intuition that nylon on that part gives a better purchase on the teeth of the chronograph wheel with less risk of marring the teeth, though I suspect the risk of the latter is pretty darned low in any case.)
I think the warmth of the domed Hesalite crystal is a big part of the appeal of the classic Moonwatch- of course, what some people do is source a display caseback for their standard solid caseback Speedmasters. ;-) . Best of both worlds that way. ;-) .
Jack