my story is very similar to yours Replican't.
i probably would have picked up a 9 if i had a choice, but the 40 was the first one i saw, so it went home with me.
i had been carrying my Kahr K9 due to it's size, but never really liked the trigger (even after sending it back to Kahr for the Elite trigger upgrade). being all steel, the K9 is also a little on the heavy side for it's size.
always wished someone would make a lightweight polymer single stack carry pistol with a good trigger.........for me, the Shield was the ticket.
so far, i've got over 450 rounds through mine with zero malfunctions. for piece of mind, i put a little dimple on the magazines to help them engage the mag-catch more effectively.
looking back, i'm glad i got the 40. it's not unpleasant to shoot, and larger caliber isn't necessarily a bad thing when it comes to self defense