Small head-space is the whole point of a carboy (be it a glass one or a PET one like a Better Bottle). You want very small head space in a secondary fermentor to limit exposure of the wort to air and thus prevent oxidation (ideally, the carboy should be full all the way up to the neck to limit the exposed surface area).
For a primary fermentation, there's plenty of CO2 being generated to prevent oxidation. But you need a lot of headspace to avoid having tons of blowoff..
This is why most people use buckets for primary fermentation and carboys for secondary. I wouldn't get rid of the Better Bottle, I'd just use it for those beers that need a secondary.
We're not talking about a secondary, but a primary. O2 is actually a good thing at the beginning, when one is trying to encourage yeast reproduction. After that, the activity of fermentation will more than drive the O2 out of the headspace, even if said headspace is rather large.
Regarding fermentation temperatures, for most of the strains I use I like a 66-68*F wort/beer temp, due to a "middle of the road" ester profile. With top-croppers and high OG brews, I get blowoff every time, which makes sense considering I have about .75 gallons of headspace in a BB.
Contrast that to a bucket, where I have at least 1.25 gallons (2-3 gallons for the larger bucket fermenters). That extra half gallon or so can make all the difference in the world.
Call me crazy, but I just prefer buckets all around. Easy to clean, easy to work with, and easy/cheap to replace should the need arise.