I got a "B-stock" one fairly recently here, along with David G. Mine is the only Baby Bottle I've worked with, and I haven't been able to figure out why it was classified as B-stock, so consider my opinion with that in mind
I also got a fancy new preamp at about the same time (and used it with the BB), and haven't gone back and tried out all my other mics in it yet, so that may skew things, too.
I've used it just on vocals, tambourine, and acoustic guitar. It does not strike me as having a flat frequency response, but rather seems to attenuate high frequency. It seems to handle the lows well, and it imparts an up-front sound despite being shy in the HF.
I can't sing, but when I try, one issue with my voice is a very high pitched "nasally" ringing thing, and the Baby Bottle conveniently ignores that part, making my voice sound almost listen-able. I also like what it did with the acoustic guitar, although there certainly wasn't much "air" - this was fine for the piece, and was probably better than bringing in a bunch of pick noise, etc., keeping the guitar as a background instrument, but still somehow still up in the mix. I didn't like it on tambourine and used a C414 instead - it just ate too much of the high end. For that reason, I don't think I'd like it on hi-hats and cymbals.
I should mention - if I really want to feature a performance of an acoustic guitar, I'm going to use a pair of SDC mics, not this one.
I remember that I also tried it on bagpipes, but switched over to a dynamic, mainly just for attenuation purposes.