I used the MSD Pro Billet. Everything is contained in the unit. It operates without a box. Just three wires to hook up. You can add a box if you want more control. When my engine was dyno'd I did a comparison with the Pro Billet and a brand new MP unit. The MSD made more a little more power but more importantly the power was much more consistent than the MP unit. You could see this on the dyno. I don't know if it would make a difference under actual operating conditions.