Traded my PX4 40 in, and took home a shield in 9mm. I had already decided that I was going to part with the PX4, and stick with SW M&P as my platform to build on. Additionally I wanted something that my youngest Daughter would find a bit more comfortable than my FS, in .40.
The store had both a regular with thumb safety, and the Performance Center, I took the regular shield home. I like everything about the performance center model except for the ported barrel. If I were to get one, I would change the barrel to a standard barrel.
Hit the range the day after I got it, and ran about 180 115gr fmj rounds through it. Quite a nice shooting small pistol. Hit the range on Monday with my Daughter and let her put a bunch through it. She did very well with it, and it fits her small hands much better than the FS, mainly due to the width. Picked up 2 extra mags, and have another 2 in the mail. Will get 2 mag guts spring kits, and set up 2 extended mags as 9 round. Going to get some 124, and 147gr and see how I like a few different ammo types.
Next up is a compact, but have not decided on what caliber.