I've got the set up you describe, I purchased it for the reasons you did, I'm still undecided whether I like the magnifier or not. I reversed the flip-to-side mount to flip to the right as I'm right hand/right eye dominant, which means it gets in the way of my left eye vision when using the red/green dot in magnified if you have it flip to the left, which helped a bit, but the magnifier adds a lot of weight and I generally find myself shooting with it flipped to the side using just the red dot unmagnified.
None of this is a slant against Vortex, for the money I think the StrikeFire II and the VMX-3T are great devices, really qualify feel to them and very solid mounts. I'm just not sure I like magnifiers regardless of who makes them. That said if you want to find out if it's for you or not the only way to tell really is to try it, and at $150ish Bucks the VMX-3T isn't too painful a price to pay to find out.
IMO if I had had a do-over I'd probably stick with just the StrikeFire, or spend the money I spent on both on an Aimpoint or a Trijicon MRO, and then pick up a low power 3-9x Nikkon P223 scope for longer range work.