Personally, I don't know that I could ever trust a conversion barrel to run when I need it to, as a CCW or as a nightstand.
If the only difference between the two guns in the differing calibers is the barrel then, once it has been proven with the conversion barrel, it should be as reliable as any other gun that's been proven.
If there are other parts differences in the guns besides the conversion barrel, then the converted gun (with only a barrel change) can never be as reliable from a theoretical standpoint as the unconverted gun because the other parts are not ideal for the conversion caliber. It's clear that the differences aren't there because the manufacturer likes to spend money making unnecessary changes between calibers. No manufacturer/designer makes changes when they don't have to. The changes between the two caliber guns are there because they were found to be necessary to insure maximum reliability and functionality.
I would never use, nor recommend a conversion barrel for self-defense use unless, as mentioned above, the ONLY difference between the two calibers is the barrel or unless all the differing parts had been changed out and the gun proven in its converted configuration.