Like A Semi-Auto J-Frame

The Shield is very similar in size to my oft-carried J-Frame.

The Shield is MUCH thinner, especially when you include the holster.

The holsters also place the guns in different locations, but that could be because of difference in brand rather than in the guns themselves.

There's not a lot of difference, in GURPS terms, between my various attempts to find a great summer gun either.

In terms of average raw damage per load:
M&P 9 Shield - 64.  72 with optional magazine.
Model 640-3 - 45.  30 with .38 Special.
P232 - 48.
P238 - 42.  48 with optional magazine.

It's a no-brainer for GURPS!