I have a Gabb dual key I bought new from Mike Gabbanelli in Houston in 2011, in C and Bb. White. He put an internal mic set up in it. I have played out on it plenty. Sure I wish I had a couple of Falcons or Heritage brand. List was 1380 with a 400 discount. 195 for an R65 Sure cartridge installed. That mic install is like a battleship. Never ever a problem. I bought it primarily to carry to practice once a week in a studio we used in Manhattan when I lived in NY. It fell off an amp at the studio and the C base reeds were knocked out. It was an easy fix since they were still in the Wood frame holder. Just rewaxed them in.
This is an economical way to go double. With two boxes you could have the equivalent of 4 boxes and cover just about any key.
I have never played it with a clip on mic and always use the internal. Miced they sound terrific. J Paul uses the single keys exclusively.
Now that Randy Falcon has passed used ones are rare and expensive. Over double what they went for new.
Hope this answers your questions. Mike Gabbanelli is a pleasure to deal with and his work is exceptional.