If you look back through this forum, you'll find lots of stories of people who started with an inexpensive aluminum track bike that fit like their road bike, but then after a year or two of track racing, upgraded to a better fitting track frame.
I agree with Bicievino that you'll want more reach and probably more drop than your road bike (depends on if you are a mass start or sprint person). If the BMC is cheap and you're not 100% sold on whether you'll be a consistent track rider, the BMC might not be a bad option, so long as you are aware that if you do end up really taking to track, you'll probably want to replace it with a better frame.