Being an oldie, I still prefer my old ACME thunderers which I've had for donkeys years, metal, with a pea, but I do have Fox 40's also. Fox's just need a wash under a tap, but the Acme (even plastic) takes a bit of care cleaning if they've been in the mud. Lanyards, the loose RA type, are a must, you still see the odd 'teacher' running around with a cord around his neck, wouldn't recommend that around here!
I carry a pair of each (not mixed) carry 1 type or the other. It can be useful to have a different whistle to the referee on the pitch next to you on a council park.......you can end up with 4 teams stopping on 2 pitches otherwise! Always worth asking your colleague in the dressing room what they're actually using.
Many moons ago it was suggested that new referees learned to 'vary the tone' of the Acme before blasting off with a Fox, is this no longer the case? I can still give players a good idea of how I'm thinking with the tones of my Acme, particulary my displeasure, How do you Fox users differ the tone?