To the OP: If your plan is to practice headshots with a pocketable gun, you're going to need a whole lot of practice, quite a bit of talent, and most importantly: a very solid "Plan B". Because it most likely ain't gonna happen.
I have an LCP and a P238. I'm an ok shot, but a headshot on a moving target in a high stress situation would be nigh impossible with the P238, which has excellent sights for a small gun. Headshots with the LCP in such a situation... keep dreaming. I can make little groups with my mouseguns on the range with the best of them, but in a "real" situation... as I said, you're going to need a "Plan B".
My criteria for a mousegun are that it conceals well (LCP is amazing at this) and are reliable (both of my mouseguns, fortunately, are). There are many other quality brands of mouseguns, and broken in properly, most of them can do the job. But if you're forced to use any of these guns in a real-world shooting scenario, I think you're better off to aim COM.
Just my opinion, of course.