Well, I've had a Quattro FX for a few nights now and have given it a good go.
Good points:
Very soft and balloon-like seal - this mask is definitely the most gentle silicone mask I've tried so far. The seal is made and secured by the air pressure inside the mask with the strap pressure holding it in place spreading the physical pressure over a larger area, making it very comfortable. The size of the seal makes it fit my face very well, I have a short, shallow nose and a wide face. Other than an overtightened first night I've had no facial marks in the morning. It's a great seal too, a seal that's comfortable at 15hPa doesn't collapse at 4hPa for the ramp, so once adjusted for your pressure it's a nice quick fit at night.
Fits low on the nose - it secures into the indentation under the bottom lip so isn't up between the eyes but is kind of halfway up your nose, if you've got a sore there from your other masks, this could help provide relief, and there's no hard plastic in that area either it's bridged from the sides with ultra thin silicone.
Clever spring frame - this seems to move the pressure from the straps away from the front of the face and spreads it more evenly, I've only had any facial marks from the straps on the first night because I overtightened it. The springy plastic has a fabric cover that is very soft on the skin.
Noise - this is as quiet as the Sleepweaver and by far quieter than the rest of my collection.
Quick release - always handy.
Bad points:
Being picky really, if you don't get the seal just right it will slide up your face and then leak from the nose into your eyes, it's really important to have a dry, clean and grease free face and seal before fitting.
The low fit means if you nostrils collapse easily this may make it worse, move it up a bit (or possibly try a bigger size)
Venting - your bed partner may not want quite that much air hitting them in the face, but it's not really a side-sleepers mask so maybe not a problem
Other observations:
The "Swing down to fit" is great, until you really need to itch your nose and have to remove and refit it during the night, it's not an easy thing to refit as you have to undo both bottom clips to fit it properly.
I'm not yet comfortable sleeping on my side with this mask, the seal is easily disturbed by sideways pressure but I'm in a Hotel at the moment and my firm sculpted pillow is at home, so I'll reserve judgement until the weekend.
Headgear is a bit small for me, but I'm told they stretch with time (Thanks TF!) so again will reserve judgement for a while...
Compared to other masks:
Far more quiet than the F&P Forma, and less heavy and cumbersome. Slightly heavier and bigger than the ZZZ mask type cheapies but a much better fit.
Conclusions:
I really like it, I don't need a full face mask most of the time but sometimes just can't get to sleep due to congestion or hay fever stuffing up my nose and I prefer not to over use decongestants. The complete lack of marks on my face is a revelation, the Forma leaves mask marks, the sleepweaver leaves strap marks, this has for the last four nights left none at all. No face marks and a great night's sleep make a great combination.