Ceiner makes a decent, relatively inexpensive kit but he is a pain in the A$$ to deal with if you need parts. Marvel has two awesome kits but are fairly expensive. The top end unit is full competition capable with guaranteed accuracy in the 2" (maybe 1") range from a rest at 25 yards. The less expensive model is nearly as accurate but doesn't carry the guarantee. These also have a last shot slide open capability which is something most other kits do not provide. marvel also makes a kit for the wide body 1911s which is the only one I know of for these models. Kimber is offering a conversion kit but I don't know if it is their own or merely someone else's with their name on it. There is another one out there but I can't think of it at the moment. I'll reply if I remember it.
I have the kit sold by Kimber - and it's a decent kit. But it has some issues - and I understand it used to be made by Ceiner and now is made in-house by Kimber. 2 issues - slide does not lock back when the last shell is fired. The kit, as configured, comes with 2 plastic magazines that will not fit into the magazine well on the gun - if you have a deep well mag - like on the Kimber Gold Combat Stainless. The fit problem has to do with the bevel on the bottom plate of the mag. The upside - is you can get metal mags that will fit fine from Brownells - and you can sell the plastic mags that come with the kit to someone around that has a gun they will fit and get most of your money back. Kimbers solution to get the mags to fit was to advise me to take off the deep well mag on the butt of the gun ....... The original Ceiner kits did not have this problem when they were making them for Kimber.
Having said all that - I think the kits are a good thing. You can shoot 1 gun - and you still have the weight and trigger feel of the gun - although not the recoil as a .45. Some of the grandkids really like to shoot the Kimber with the conversion kit on it vs a stand alone .22 semi auto that I have - they just like the looks and feel of the bigger gun I think. But a conversion kit is a good way to practice for next to nothing vs putting 4 or 5 boxes of .45 ACP thru a gun.