The impact itself is not going to bowl him over (otherwise the shooter would be knocked down when firing as well - basic physics) but the blunt force impact will shock his nervous system as well as knock the breath out of him. At the very least, the armored attacker (remember, actual criminals now show up in illegally obtained body armor too) is suddenly going to have other priorities for a while. Like trying to breathe with a shock-paralyzed diaphragm.
So, yeah, not likely to penetrate Kevlar but the recipient is still not going to be able to continue the engagement for at least several minutes.
I concede to the basic physics part, but the shooter is braced, or should be. It makes a difference. You can see the effects of not being braced on YouTube. One in particular response to Biden’s Shotgun comment. It is very funny.