I have heard mixed reviews on conversion kits. Some, the mag well will not work properly, depending on the manufacturer of the lower. Other complaints I have heard was the it never cycled correctly. I cannot speak to any of these, as they were all second hand info to me. But, it was enough to turn me off of getting a conversion kit.
I have considered a dedicated .22 upper, but I think ultimately I will simply go with a .22 rifle altogether. The difference, for me, is roughly $100-so, its sort of a no brainer for me.

I would suggest either a dedicated upper (again, check that the mags will work too), or a separate rifle. I have heard too many bad things about conversion kits, and I would want to ruin my AR with a bad choice.