I recently bought both in California when they appeared back on the list. I didn't want to miss out on the opportunity to have the option of either down the road. I have a CCW and have the .40 on my license. Both have been flawless on my reloads and of course factory ammo.
I'm 6'8" with large hands. I must be careful changing mags with either cal. The meat of my palm fills in the space below the rear of the grip with the mag out and if I'm not careful, I'll get quite a pinch slamming a fresh mag home. This is common for me with other autos with a short grip frame.
I think they're both great carry options. I really prefer my M&P .40 and my Kimber .45acp ultra carry II overall. Much more comfortable in my big hands and no pinching, but heavier and larger to carry
Can't go wrong with either Shield in my opinion.