This has been talked about endlessly on one of the Glock forums; discussed by some folks that are genuine experts on Glocks. After one dispenses with all the "I think this or that" because of "this or that", it boils down to personal preference.
I have them in all five of my Glocks. I like them and like the looks. I pulled one of the plugs on evening, just to check on something. After over 3,000 rounds through that particular Glock, there was not even a trace of powder residue or any other dirt, residue or debris in that part of the grip.
If Glock designed this void in the grip to hold the stock on a full automatic pistol designed to be used in CQC situations, you'll have a bit of trouble convincing me that plugging that hole will yield to any problems or issues whatsoever.
I no longer trust my government to act on my behalf.