Well it's the cheapest way to add 22LR to your .223 AR but overall pretty good if you don't need real accuracy. Probably the biggest thing is to research the competing designs and choose the one most reliable - and with the best magazines. You don't want to have to change hammers, springs or any other parts except what's obvious like the bolt carrier group and magazines.
I've heard firing a huge amount of .22LR can gum up the gas system but haven't seem any real proof of it.
I debated over this myself for a long time and earlier this month went with a dedicated AR-style .22, the Colt M4 copy by Walther. S&W, SIG and Ruger of course have their own designs. Your method is half the cost and is a true AR with the controls more like an AR. All the solutions can be picky with ammo and you have to find a brand that works well.
Let us know which direction you go and how it works out for you!