The Kimber, Ceiner, and Marvel's Unit 2 are meant for combat practicing and are configured to operate with the sights on the slide which moves in recoil. Their accuracy is significantly less than the Marvel unit one.
There are some units in which accuracy is degraded, I am sure, but even the Ceiner, cheapest in dollars, is in most cases more accurate than the host pistol was, in centerfire.
Be careful, Click, if you order a Marvel: more than once, I have heard of shooters ordering from them, and not getting what they thought they ordered! One of the units works just like the Ceiner; it's 'OK', but the other, as LD describes, leaves the barrel, and most of the slide, rigidly attatched to the frame, of the host pistol, with the breech block only, reciprocating, like the 41 Smith. This is the one you want, for accuracy.
What's gonna be on top of???
P.S. The S&W 41 is only the standard for "currently produced" rimfire pistols; High Standard (Hamden) built better, more accurate, pistols, but they are out of business!