I've got 2 BKG in my 2.5ft tank, got them both...maybe a year ago? can't exactly remember but when i got them they were 2", now one's pushing 9" and the other 6-7". They are extremely peaceful with other fish, doens't figt with them, just slides inbetween these rock cave things that I made for them.
However, they do get aggresive with their own kind. My smaller BKG has broken fins and well, smaller because he's been bullied by my other one, which eats well and has perfect fins and colour, therefore grows faster!
I recommend some, btu makes sure they all have places to hide because from my experience, they will get abit nippy! But otherwise, they are the best fish I have at the moment!