If you are just polishing you won't be changing the angle. The sear engages the forward facing part of the nub (it holds the striker back) and the bottom downward facing part of the nub rides the top of the sear. The bottom facing part on the new gen striker has a raised flashing line that I try to polish out. I may lightly stone it to help, but stoning can certainly take material off.
I agree! When I installed my Apex kit, I polished the trigger bar surfaces. I can't tell how much difference it made, but I am happy with the final result.
There are several sights that fit or just over hang a bit, I beleive the Tru Glo's fit if your into those.
On the striker nub, are you talking about the projection that comes down from the striker out of the slide? How did you avoid changing the firing pin/sear engagement angle?
Does anyone know what night sights fit the Shield? I have seen other report that the Trijicon SA37 fit. I was wondering if the TruGlo sight for the regular M&P fit the Shield.