I've had a M&P9c since they were first introduced. I managed to buy a 9mm Shield a week after they were announced.

My Compact is my daily off-duty gun. My Shield is my BUG while at work. The Compact is just too thick for vest carry. But the Shield is a dream for this type of carry.

I have RCS Phantom holsters for both guns. I carry OWB over my kidney at about 4 o'clock or so. In this type of carry, they are about equally concealable, so I carry the compact. (A good belt does make all the difference!)

I shoot the compact slightly better than the Shield. But don't take this as a slam on the Shield. With the Shield, I can clean the 6" pie plate rack at 25 yds, using mandated frangible ammunition, at my agencies facility.

Shooting the 9mm Shield, I quickly forget it's a compact gun designed for a specific task. One quickly starts to compare the Shield to full size platforms. It shoots that well.

OP, we all have different size and shaped bodies. The best thing you could do is to shoot both. Carry both and see which works best for YOU. You already own a Compact. Buy a Shield if you can get one without paying scalper's prices for it. If the Shield doesn't work out for your needs, you would have no problem selling off a Shield right now.