VIDEO HERE (7:24 minutes)
*****
In the video, he talks a little about the unreliability of 22LR ammo, which is the main reason, based on my own personal experience, I wouldn't consider a 22 for even a back-up gun.
I cannot even begin to tell you how many misfires I've had using 22LR. Granted, I've shot a lot more 22 than I have any other caliber or maybe even all other calibers combined, but I cannot recall ever having a misfire on any 45 ACP. I do remember getting a 22LR bulk box of 550 rounds once that was giving me at least a couple misfires from every 10 round magazine. I thought it was the gun at first, but I switched ammo and it ran fine.
I've also gotten a few hangfires from 22LR and I've never gotten that from centerfire ammo.
I will say that the huge majority of ammo failures came from bulk boxes although I remember having a box of CCI Stingers that I trashed because I had misfires on 3 or 4 out of 10 rounds in a single magazine when I was shooting ground squirrels, but that was years and years ago. I haven't had an issue with CCI since, though.
Now, all that being said, here's another video from Lucky Gunner where they're addressing the issue of unreliable 22LR ammo.
Is .22 LR Too Unreliable for Self-Defense? (7:37 minutes)