Sizing Instructions for Masks

[laurie2025]

Currently I am using nasal pillows and am considering a FF mask to have at hand when I get a cold or sinus issue. My mouth would also fall open if I let it, so I tape and use the nasal pillows but feel I need a FF mask for backup. I am concerned because I don't want to invest a lot of $$ in a mask that won't work for me. Even if I get a few from cpap.com the return insurance and shipping will add up quick.
Anyway, I was wondering if anyone had used the sizing instructions offered at cpap.com, to help them get a good fit, and what was your experience using it? I was reading many posts about bruises on foreheads and masks pressing here and there, and a lot of leakage, so I wonder if those sizing instructions offered any help in at least paring down the choices.
Thanks!