[gomerpyle1107]

I have a M&P9 full size with a 5 inch barrel and a compact with a 4 inch barrel. Can I swap sides between the two? I put the 4 inch side on the full size frame and it seems to function but I hesitate to fire it.

 

[Canyon Man]

Yes you can. Good to go !

 

[ctr1970]

If it's a Gen 1 slide on a 2.0 frame .. yes it will work. The slide will lock back..

Using a M 2.0 slide on a 1.0 frame.. it will work. but won't lock back the slide on last round, nor will you be able to lock slide back normally.
The slide cut for slide stop is longer on the 1.0 slides.

 

[zod]

Yes. There are a few videos on youtube that cinfirm this also. One is from Provectus Group about the new oem flat trigger. He is running a hybrid FS frame with compact upper assembly. Can't link the video for some reason.