I have been talking about this with a USPSA-shooting friend who is encouraging me to join him in his fun. I am thinking of the little red dot sights, like the Burris Fastfire and Leupold Delta Point. I assume these will throw me into some competitive never-neverland, but if you are just wanting to shoot and not concerned about what category your scores happen to land in, it might be an option. At my age, I am not at all concerned about scores and competition, but I do like to shoot.
I can't see something like the Merit device working for me in a game like this where you are constantly moving around. The problem I see with the dot sights is that they are expensive to mount them properly (usually requires milling your slide to get them mounted low and sturdily), and if you want to shoot more than one gun, the expense would be multiplied.
I will be interested to see what other USPSA-shooters have to say.