I read that vinegar was the best stuff for storing epoxy brushes, that it didnt dry out over time like acetone.

has anyone tried this, does it work, will it be ok even for a "finishing" brush?

I don't follow I'm afraid?

All I use is epoxy and 90% of my work is in carbon, if you introduce something to the brush i.e. the vinegar then you have the issue of ensuring it's all removed prior to re-using the brush otherwise it will contaminate the laminate and potentially cause problems down the line such as non cured sections, delamination or surface imperfections.

or just use really cheap throw away brushes