I have the 9mm. We haven't put too many rounds through it but will add some this weekend. My 14 yo son enjoys shooting it, he can't hit anything with it but the recoil is very manageable. It's a little more flippy than a full size gun but again controllable. This was all with Speer Lawman 124gr no defense loads yet.
What I didn't/don't like:
Gritty trigger pull - I used 1200 grit Silicon Carbide coated paper to polish the working edge of the transfer bar hump that pushes the striker block up. I was very careful to maintain all the angles but just made it a little slicker. It probably would have worn in eventually but I wasn't willing to wait. This helped but I will probably put the Apex USB in at some point, just not looking forward to removing the rear sight to do it.
Slippery grip - The Shield looks like it would be very rough to hold with all the texturing but mine feels slick so I will be getting some abrasive tape soon. I think that might help a little with the muzzle flip.
Extremely difficult to load magazines - my 7 round magazine was nearly impossible to load and the 8 round was pretty stiff. I disassembled both and put a very light application of Balistol on the front and rear of the mag. The spring on the 7 round mag was not seated properly on the follower causing it to bind. After reassembly my son was able to fill the mag without any assistance.
Now he can load for me while I shoot
There were also some sharp edges/burrs on the bottom of the grip edge. I use the sand paper on them as well.
Just showed it to a friend who has a full size M&P and a Ruger LC9 that he carries. He said the grip felt much better than his LC9 FWIW. I've shot the LC9 and it was fine but I think the Shield is more comfortable and controllable.
Overall it's not perfect but it's a keeper.