The LaRue LT-755 Flip-to-side mount is the best option. It keeps the magnifier on the rifle, and it functions quickly and easily. The mount is pretty tough and secure. It's better than the Aimpoint mount which requires that you have to remove the optic. You have to make sure you get the right mount for the PRO, which is pretty much an absolute co-witness (just an RCH off, but for all intents and purposes it's absolute)
I'd also recommend getting the Aimpoint 3x magnifier. It's pretty durable and very good optics for what it is. Keep in mind that with a magnifier, you're really cutting down on your FOV, and it will slow you down on rapid shots. Unless I'm shooting from prone or barricade, I will only use my 3x beyond 50yds.