I have the ALG mount and a T1 on a Gen 4 G17 and have a few hundred rounds through it. Here are my impressions based on how I shot the gun so far, which was static at ranges out to about 60 yards in daylight.
1) The T1 improves acuracy and ease of shooting at distance - particularly over 25 yards as there is much less eye strain. I got decent hits on 6" plates at 60 yards first time out and the misses were close.
Groups at 10 and 25 yards are smaller too - and just easier. You could argue this makes a G17 almost AK47 accurate inside 100 yards.
2) Once you pick up the dot it makes target to target transitions easier and faster - think plate rack or dualing tree type situation. Its nice how the dot stays put on recoil.
3) Picking up the dot on presentation is slower for me now vs irons, but adding a cut down smallest Glock Gen 4 OEM backstap made it easier as the glock points more naturally.
4) I feel like the T1 gives me better visibility of the target area than irons as I dont have to focus on the front sight.
5) FYI - this gadget replaces the glock backplate and restores your ability to rack the slide off a belt etc and is easier to remove when needing to service the gun - so far so good.
https://www.wrightshooting.com/tacrack-.html It also looks fucking cool like an MP7 charging handle - so natually the chicks dig it.
Finally, I weighed the G17 with the ALG mount, the T1 a Surefire X300 and no mag it came in at 33oz which is 6oz less than an empty 1911. Yay technology!