I'm thinking about getting a Bb bass trumpet. Can anyone with this experience tell me the pros & cons of playing both the bass and standard Bb trumpets?

Well, I play the Gentzen bass every now and then. You'll probably never need it on a real gig and if you do, a bone usually will cover it. Pros and cons... well, the cons are the tuning and sound. The pros are increased air support and a nice workout for the bigger muscle groups. I like the bass because it is a bigger mpc and uses more air and lets me just blow without the resistance of the Bb. Anyways, just my two cents. I do think there are some positive aspects to playing bass/baritone/trombone for trumpet players.

Am I assuming incorrectly that one could play the Bb bass trumpet off of a regular Bb trumpet music sheet or score?

Correct, just sounding will be 8vb.

Properly played, the bass trumpet will sound like a trumpet. Alexander makes great bass trumpets (in Bb and C) but they are pricey, and unless played correctly will sound like a cheap baritone anyway.

I play tuba and tenor horn (bavarian folk music - accompanying a diatonic accordian) from time to time and it does not affect my trumpet playing at all. If anything, it is a great warm down after some heavy duty trumpet practicing.
Finding a bass trumpet that is in tune will be your biggest challenge-then the trumpet player things like what mouthpiece, embouchure and support will eat your time up.
In any case, it sounds like fun. Let us know what you do!

Thanks to BEAR, VULGANO BROTHER, AND ROWAK for your input about Bb Bass Trumpet. I'll announce my find when I get one...............crowmadic