For my ears OK1 has more detail and spaciousness but you do not get the isolation that you get with the RE252.
Yesterday I compared in an airplane trip the isolation of the RE252, ER4P/S and Westone E3X.
ER4P/S are the ones that isolate the most but they have their sound profile and some people are unable to wear them.
The isolation of the E3X and the RE252 is similar.
For some music and mind states I woudl prefer one or the other.
It seems to me that the RE252 gives...