You misunderstand the purpose.
They were designed to do two things:
1) change the grip angle of the Glock to more like a conventional grip.
2) add a beaver tail to mitigate slide bite on all generations of Glock. The GFA preceded the Glock factory beavertail back straps.
They change the grip angle by filling in the hollow between the tang and the hump on the lower grip so they do make the grip bigger but on a Gen 4/5 where you are staring with a “small” grip it’s not that much extra reach.
On Gen 3 and older guns where you are starting with a “medium” grip it makes it it a large.