I have one and love it. If you'd like to try it out, we can get together at a range and you can abuse it all you'd like.
For me, being a lefty and 6'2"/200lbs, the 3/8" width wasn't enough to sway me toward the Shield. When the shield came out, all of them had a right handed safety. It was also missing the lefty-friendly slide release on the passenger side that the 9c has.
With the short magazine, the grip is actually a bit shorter than the Shield. Wider, but shorter. The wider grip puts a little more in the web of your hand which makes it feel a little less snappy than a single stack.
In comparison to the Glock 19, comfort and how well it naturally pointed were very similar. The G19 being slightly larger. Between the two the most noticeable difference was how much more comfortable the S&W trigger safety was compared to the Glock over an extended range session. Maybe I've got girly hands but after a hundred rounds or so, the Glock safety starts to feel a little coarse compared to the S&W that uses a trigger that is split horizontally and feels like a single piece one pressure is applied.
With the current mail in rebate, the Shield price is almost half what it was when introduced ~five years ago.
All of that said, I have no regrets going with the M&P9c BUT... If I were in your shoes, I'd go with the Glock 19. You know the design. You have magazines that will work in the 19. You're familiar with the take-down and maintenance and the 19 probably has better resale than the 9c if you ever decide to part with it.
You're still welcome to try mine

.