"-Mags- The MK1 uses a different mag. They can be harder to find and more costly when you do"

Nope. They are easily found. The SM, MK I, and MK II can all use the same magazine with the slot on both sides. And I think Mk III mags will work fine in any of the earlier Rugers. You just need to swap the follower stud side, about a 30 second job. The Mec-Gar mags work fine, about $15. I have an original SM mag, a MK II mag (Mec-Gar), and a MK III mag. They are all OK in my SM.