I have the Ciener conversion with target sights on a lower that I bought through Shotgun news. It is very accurate but not reliable with low power ammo. One of my hunting buddies who shoots bowling pin comp. also has one and loves it .
The one I use the most is a target-sighted Kimber conversion on a Kimber stainless frame and it has proven to be quite reliable and accurate. It will function with standard velocity long rifles, but really perks with high velocity fodder.
I also have a blued Jarvis conversion unit that works well and has a slimmer, lower, slide profile. That unit requires high velocity ammo to function properly, and actually may be more accurate than the Kimber unit. It uses Colt Ace magazines whereas the Kimber requires a proprietary magazine. Sadly, I believe Jarvis no longer offers it.
Be aware that some of the new entries in the rimfire 1911 market, like Chiappia and GSG, sell complete guns for little more than what good conversion units are going for.
I have the Ciener with fixed sights that I use on two different Kimber guns and it works very well with all ammo I put through it. The only thing I don't like about it is it doesn't lock the slide open after the last shot.
I have shot a friends GSG and I really liked that. If I were to start over again I would go that route. Key
I have a Kimber conversion. It has a penchant for the high velocity ammo. With that, it will shoot to ~1-1/2" at 25 yards, if I do my part. Standard velocity ammo will shoot a bit more accurately, but not as reliably.