I recently got this grip plug from the Glock Store, which adds over two ounces of weight to the grip, and functions as a grip plug. Watching the dot move, this added weight definitely makes a difference. Best $30 I have spent (lately) on improving how a Glock shoots. Available for all gens, but the G4/5 part is what I wanted since I haven’t seen them available elsewhere — you had to get a G3 and modify it to work.
https://www.glockstore.com/Thug-Plug