I have. A guy at work (IT dude) bought a gen 3 G21 police trade in and asked me to look it over. I tore it down and cleaned it good and took it to the range. It had the OEM Glock night sights and if I remember correct, I printed a decent 25 yard group with it. I thought I posted that pic on here. I'll look and see if I did.
My G41 has Defoor sights on it and for my skills and eyes, I seem to print tighter groups with it. I would guess that if I had a G21 with Defoor sights, the groupings would be similar. My G41 is the only pistol I have ever shot a 100 with on a B8 target at 25 yards. I've come close with a couple of G17.4s. I've shot a pretty tight group with my G30s as well and I prefer the slimmer slides of the 41/30s.
On edit: Found it....post number 850 (page 85) of this thread. His trigger was just awful but I still managed a 94 with it. I only shot a few rounds through it so with a better trigger, Defoor sights, and S&B ammo I could probably turn in a high 90 with it.