Auto426, are you talking about the ones made by AI ? I keep seeing mixed reviews on those.
AI makes the steel mags. I'm not sure if Ruger makes the polymer mags themselves or contracts them out, but they seem to be the preferable option based on what I have read. The 10 round poly mag weighs less than half of what the 10 round steel mag weighs, is shorter than the steel mag, and can be topped off while still in the gun. I believe they are cheaper as well.