I like the Sparc on my SIG. The way the in the box mounts line up, it works just great. I have heard that people have issues with unintentionally turning the sight on, which may be true for them, but I have not noticed this. Of course, my failure to notice this could be due to the fact that the sight turns itself off after 6 hours.
The batteries the Sparc uses are not particularly common, which may be an issue.