I thought it was $1000 more? so yeah, if it's only $500, sounds like a good deal on the B12.
it's got the new frame. Haven't ridden it... but it looks good, and is probably a bit slipperier.
you get upgraded wheels, upgraded crank as well. The B12 will hold its value better too.
but is it 'worth it'? as in, will it make you 4 minutes faster in an Oly tri? nope. Would spending that price difference on a wheel cover, aero helmet, race tires and latex tubes make more of a difference for dollar? yup.
get the bike that you fall in love with. you'll ride it more... and THAT will make you faster.