I carry a Shield in .40 as my off duty and BUG. I absolutely love it! It has been entirely reliable with no failures of any kind with any ammo I fed it. The trigger is one of the best around.
In size, it is nearly identical in size to my PT709, PT740, and LC9, all of which were my primary "EDC" prior to the Shield.
It would be perfect it there was a .45 Shield, but I will settle for the .40.
As an FYI if you can find one in stock, Academy still sells them for $399 (this is what I paid). Make friends with the "Team Leader" at the Academy gun counter, and maybe he will call you when one comes in. Gander Mountain also has had them in stock periodically (and briefly) at $449, which is MSRP.
My favorite holster for the Shield is a High Noon Split Decision tuckable IWB. When I am dressed up, this is what I carry tucked. I have many hours of practice drawing an EMPTY Shield from the tucked position.
While a little larger, if you find one, also look at a Ruger SR40C or a SR9C. I often carry my SR40C IWB untucked in another High Noon Softy when dressed casually with a polo or other loose fitting shirt.
I have seen a lot more Shields in 9mm than .40, but my preference recently has been .40, because I can't find a similar sized .45 from any major maker at a decent price. I carry a Ruger SR1911 on duty.