If your meter had exactly the same response curve as your film, just metering through the filter would solve all problems -- but that isn't the case. Selenium, CdS, silicon, smart phone, DSLR sensor, another brand of DSLR sensor -- all have curves different from one another. You can depend on metering with a DSLR to give a correct exposure, for the DSLR you used, but not really for any of the other kinds of meters. In the end, there's a rule of thumb (at least three stops for red, four or five probably better depending on your film type), and there's bracketing and testing. If you can do so, test your film with your filter before you shoot anything important -- if you can't, then give three stops, and bracket at least +1 stop, preferably also +2.
Film costs more than it used to, but it's still cheaper than a lost shot.