I had the RM06 on mine, I like the smaller dot for distance shots(50 - 75yds) In the end, I just didn't like optics on a pistol, never have. I just thought I'd try it out once on M&P CORE 5in.
If you're going to gong steel at IPSC type distances, you may find the larger dot helpful. I just always maxed out my brightness when I wanted a bigger dot as it seems the rays of light extend out(perceptually) to "make" the dot larger.
This is a very personal decision that I'd highly recommend you seek to observe in person before committing to a potentially costly unhappiness. Best of luck!
-G45