In another life, I used to work for a bicycle manufacturer and part wholesaler. Unfortunately it was before roller brakes became popular so I can't really speak to their pros/cons.
Honestly, I would recommend going to your local dealer for the Birias. Mom & Pop bike store owners are generally a good group of guys and are straight shooters. They know all the ins and outs as they sell the bikes, service the bikes and ride themselves. It is in their blood.
General mark up on a bicycle is about 35%, so feel free to wheel and deal a bit as well.
EDIT: Keep in mind bike shop owners are NOT in the business to get rich. They certainly aren't making a killing by marking up 35% on bikes. Some may negoticate price a little, others may not.