It probably sounds irrational, but I avoided full face masks in the past out of a fear of asphyxiating if there was a power blackout during the night. It turns out this mask has an anti-asphyxia valve that is forced open if the machine turns off for any reason (something they probably should promote but don't seem to in their advertising!). I did a test and was able to breathe fine with the mask on tight and the machine switched off.
The seal took some experimentation to get the right tightness via the straps, and the right setting for me via the adjuster dial located at the top centre of the mask.
One trick I've discovered is to make sure you only position the full face mask on your face while the machine is off. That way it creates a suction when the pressure starts to flow and basically "sucks" the mask to your face. If a leak develops at any time I just turn the machine off, reposition the mask, and go again.
It's like all cpap masks/machines - what works great for one person may not be the solution for another.
Personally, I'd never use nasal pillows again even if Resmed promised me a lifetime supply of their latest version. But others swear by the pillows and detest the full face face mask. It's about experimenting to find the right solution for you.