My situation is similar to Brian's. I have had an Amado water key on my Egger trumpet for many years, and aside from a little friendly kidding from other trumpeters, no one else has cared. I'm not sure anyone else in an orchestra has ever noticed, maybe because I had it placed near the point where the bell is wired to the bow. I know a couple of other players who have added water keys to their Egger and Naumann trumpets.
As far as being a no-no, for me that would only apply to a authentically produced no-holes instrument. Vent holes are a modern adaptation, so why not a water key?
