There are different ways of looking at this. Each depends entirely upon YOU!
First, a .223 can do everything a .22 can and MORE. Hence, maybe you don't "need" the kit at all. Or you could carry a good quality .22 HANDGUN!
Second, the Ceiner is a great way to practice and train with the SAME weapon. It would allow you to carry a lot of .22 ammo and not have the added bulk of a second weapon.
Third, you could carry the .223 and if you are not alone, the other could carry a .22 LR such as a 10/22 or other good quality rimfire.
Fourth, I use an ALEX CARTRIDGE, some other companies make something similar. What it is, is a chamber adapter the size of a .223 cartridge that allows you to shoot .22 LR IN your .223. It is a single shot and slow to operate, BUT if you feel you will only shoot once in a GREAT WHILE, it works well. You could have it loaded and in your pocket at all times. Open the chamber and slip it in. The recoil probably doesn't cycle the action, so you pop it out and rechamber a .223 round and you are in business.
Just trying to give you some options!
The Ceiners are good units from everyone that I ever knew that had one for an AR15/M16. You can definitely trust them.
Good luck!
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Plainsman

primitiveguy@hotmail.com