I have not messed around with the AK filters too much on the ES100 but I noticed the differences when I used the same AK Filters on my Cayin N3 DAP. It was pretty noticeable. Some worked well with my headphones and some did not. Did not like using sharp filter with planars, but I did for dynamic drivers and hybrid IEMs.
I used to have the N3 also (sold it after getting the ES100 because redundancy). on the N3 sometimes i used the slow one for acoustic or soft folk songs in the beginning, but after a while i settled for the sharp roll off filter on it. the N3 has a "fatter" and warmer amp sound to me, so it's better with that filter. on the ES100 it sounds cleaner, to me the short delay sharp roll off is better. also on the ES100 the effect of the filter change is more noticable than the N3