I can't speak to the Shield but I've done the trigger pull on my FS M&P9. Mine is a bit more involved since I have the mag safety.

The only difference i see is that if I use the lever, it stays down until I insert a mag. When I reinstall the slide, the striker ends up uncocked. If i do the trigger pull, the striker ends up cocked.

While I have practiced doing it with the trigger pull (just in case), I rely on the lever for routine maintenance.