The Brava 4.15 uses the billet system and the Ignite K3 uses the Cast system. The 4.15 has a little more stopping power, but both systems are more than enough for LO206 racing.
I’d recommend the Ignite K3 from Fastech. The baseline set-up window is very wide, which eliminates the need to make adjustments right out of the gate. This will allow you to focus on driving, your hands, feet, etc. The important stuff! :)