Absolutely not. I've been rehearsing steadily with four different performing groups of at least 12 to 18 people, since at least June of last year, and part of the reason why this was never required for us is quite simply because enough musicians simply refuse. Those masks are dumb and the bell covers are even dumber. I absolutely refuse to put something so stupid on a high quality professional instrument, just as I would refuse to be told what kind of valve oil I must use with it. There is not one single documented case of anyone ever contracting a virus via a wind instrument, in recorded history - and certainly not in the last year. Not even one.
Some who truly believes they are at risk should not be there, period. I really don't blame anyone for making that kind of a choice. I really don't blame anyone for doing anything they truly think they need to do to protect themselves. But I seriously question compliance in violation of one's personal and professional principles - whatever it is. I just can't do it. I won't do it. And nobody can make me. Here's something you CAN believe in: I will still find a way to play with other like-minded professionals who will not compromise their personal integrity either, some other way.