the difference is noticable if the length is just outside of your range. If the rider is something like 5'4, they are much more likely to notice the difference between 170mm and 172.5mm. They should be on 165mm.
might as well try crank lengths with a cheaper crankset, like sora or tiagra, than play the swapty swap with DA. much easier on the wallet that way.
for a 52cm and under, you want generally want 165mm cranks.
or something like 18~20% of your inseam.