One exciting aspect of NTSYNC is that it could get into wine upstream. FSYNC is only available in Proton and not in upstream wine, mainly because it is not full

One exciting aspect of NTSYNC is that it could get into wine upstream. FSYNC is only available in Proton and not in upstream wine, mainly because it is not fully conformant, i.e. it doesn't behave exactly like its Windows counterpart does. But NTSYNC doesn't have this problem.