I have to say, I did not like my BB at first and actually returned both of them!
Jackson was in between a 5 and a 6 and so I bought both and could not decide between the two, but the difference was substantial between the 5 and 6. One looked a lot bigger than the other... I was very "ehhh" about them and after paying $80, "Ehhh" wasn't good enough for me so I returned them.
Probably 7 months later (this past October, I think) I don't know what came across me but I decided to try it one more time, going with the size 5 and now I'm in love! I don't know, it was kind of weird, it took me a while. Now it's almost the only harness we use....
I went with 5 because the 6 had a "bulk" where the d-ring was and when I'd buckle it, it would bunch up if that makes sense (because on the 6, it had to be tightened almost all the way) whereas the 5 it's on the loosest end (either hole 1 or hole 2) so we have more of a "centered" harness.