For completeness sake, if however you get a new chain fitted with that 12/25 then there is a chance it would be a link small if you ever wanted to swap back.
For completeness sake, if however you get a new chain fitted with that 12/28 then there is a chance it would be a link small if you ever wanted to swap back.
And posted that as I wanted to be clear that it was fine to go from 11/28 to 12/25, but that does not imply it would (always) be ok to go the other way. So if (s)he got a new chain fitted to that 12/25 and it was correctly sized for that there is the chance that new chain would be a link too short should the OP then try fitting the original cassette back on.
Anyway I switched both my road and tri bike from 11/28 to 12/25, no issues because if it works on 11/28 it can't not work for 12/25. I also use a 50/36 chain ring so I have the holy grail of sequential shifting and minimal overlap. Best overall combo for low powered flatlanders such as myself. "They know f_ck-all over at Slowtwitch" - Lionel Sanders