As with almost everything in this hobby “it depends.” As a general rule
though, I would say to NOT rely on the parfocal-ness of filters for tack
sharp focus. I’ve read in other places that the refraction properties of
the telescope optics may affect the focus point for different wavelengths
of light, so even if the filters are parfocal the scope optics may cause
differences in focal points (or something like that…I don’t understand
all this either!).
I have astrodon filters and for a long time I simply used the LUM filter
for focus (without offsets) because I thought the filters were parfocal.
Since I’ve started using offsets I believe that my focus has improved, and
there was enough of a difference that even my parfocal filters benefited
from using offsets so that the focus points are slightly different for each