Yes, I'm using the Quattro Mirage and have tried the F&K Simplus. For me the Quattro is the best but I suppose the shape of a person's face makes all the difference in the world when it comes to trying to make a seal with these devices. I can well appreciate the challenge a manufacturer has when trying to make something that will work successfully given the wide range of facial shapes it will encounter. My skinny bony face is particularly hard to fit.
Yes, I have experimented with mask liners have come to the conclusion that they don't really make for a better seal, but they do make having leaks more tolerable by diffusing the leak so that it doesn't sound and feel as objectionable. That's all well and good but I think even more important is the fact that a mask liner can make the mask feel more comfortable. Often perception is more important than reality. I don't currently use a mask liner but for those who do I'd say if leaking is below the allowable level and a liner knocks the noise down to where it doesn't bother you and keeps the air out of your eyes, then go for it. Of course we would all rather just have a leak proof mask but then, as the old Rolling Stones song goes, "You Can't Always Get What you Want".
As for the gel pads for nose bridge protection, I haven't tried them yet but probably someday when the need arises. In the mean time, I have found that a small patch of soft cotton placed between the nose bridge and the mask allows me to wear the Quattro mask pain free. YMMV but it works well for me.
Having made the mistake of thinking the Quattro Mirage could be used at 20 cm W.C. pressure earned me a very painful nose. Believe me, I tried all possible combinations of loose, tight and all knob adjustments. This mask and my face do not lend themselves to sealing at any pressure over 18 cm W.C. I have a fairly slender facial structure and the mask tends to bottom out on my cheek bone before both it gets sealed below and above it. You'd think the knob adjustment could compensate for that but don't count on it. When I finally accepted that and set my upper limit to 17 cm W.C., all my problems went away and I'm impressed with how well the Quattro can affect a seal that will tolerate side sleeping with no worry about leaking. Now I am able to install it as the manufacturer intended and have it float on the air cushion. It just won't do that at the 20 setting on my particular facial bone structure but i can live with that. Fortunately I don't need it to go that high since I am getting AHI's of 1.4 with the 17 setting. Pushing the upper pressure limit was causing the mask to have major leakage and that started the S9 and the leak to feed on each other and completely lose control of the situation.
Thanks for the info on the F10 and the FX. I may get around to testing those some day if my needs change. I have found a supplier that allows for free trial testing of masks so perhaps I'll try some others if/when I need to bump the pressure up in the 20 + range.