.22 conversion units have their place - but it's limited.
I have used a .22 LR conversion unit with this 16" carbine:
It's 5.6 pounds unloaded when set up for .223 and a bit lighter in .22LR. A Ceiner .22 LR conversion unit and a couple magazines doesn't add much extra weight.
I carry it broken down in short case that takes up little room in a baggage compartment in a PA-18 and will even fit in the very small baggage compartment in a PA-12. With a 1-12 twist barrel it's accurate with .22LR.
The advantage is that you can carry a magazine of .223 for larger game, and then also carry a couple hundred rounds of .22LR and the conversion kit for smaller game. .223 Rem is not only overkill for small game, it's also obnoxiously loud where a standard velocity .22 LR isn't.
The Kimber .22LR conversion is pretty popular and readily available. They are however not always a drop in fit on a 1911 and you may need to get another slide release lever to fit to the conversion unit.
I'm also in general agreement that if you want a .22LR pistol, just buy a .22 LR pistol. However, if you've got a spare 1911 frame sitting around, it's not a bad way to go.
This one is set up as a dedicated .22 LR on a JPE frame that I used to use with a slide and barrel in .400 Corbon. Properly fitted, it is very reliable and has decent accuracy.
Arguably the best .22 LR conversion kit around is the Cadet conversion for the CZ 75. It works on both the full size and compact frames.
It's relentlessly reliable and very accurate:
It's not something that will beat a S&W 41 in a bullseye match, but it's up there with a 22/45, and like the Kimber conversions, it offers the advantage of having the same controls and trigger as the centerfire version of the pistol.