I've spent a couple nights on the Synmat UL7 now, so I thought I'd share my early opinions on how it compares to the NeoAir.
Fabric:
The Synmat UL7 fabric is definitely softer, quieter but more slippery than the NeoAir. The NeoAir uses a grippy sorta rubber feeling nylon, while the Synmat is a softer/quieter nylon which feels nicer on the skin, but it's also far more slippery. I kinda like the slipperyness between my body and the mat, but not between the mat and the tent floor. If you used the Synmat UL7 on a slippery floor like silnylon then you'd likely have an issue that would need to be address with silicone dots or a similar strategy.
Dimensions & Shape:
The Synmat UL7 is a bit wider (maybe 1") and slightly longer (maybe 0.5"). The extra width is a nice, although 1" isn't a huge difference. I do think I prefer the vertical Synmat baffle orientation rather than the NeoAir's horizontal baffles. This is the main reason I got the Synmat and I think the horizontal baffles + 1" of extra width maybe makes the extra weight worth it.
Warmth:
The Synmat seems warm to me based on two nights around freezing, but I also find the NeoAir to be quite warm. Both pads seem like solid 3-season pads that I wouldn't really want to use in the dead of winter without a CCF underneath, although you could probably get away with it if you had a toasty bag and a bit of endurance.
Overall:
The Synmat seems like the more comfortable pad with it's 1" of extra width and vertical baffles, for many this makes it worth the extra 2oz worth it. My Synmat does tip the scales 1oz over though (17.3oz) which is pretty much in NeoAir large territory since that mat normally comes in under it's 19oz spec. So some people might just want the NeoAir large. I'd be a bit worried about using the Synmat UL on silnylon without a silicone treatment, so Tarptent/SMD et al users might want the NeoAir so it doesn't slide around if your tent isn't totally level. With that said, I haven't actually tried it….I'm just speculating because the Synmat sure feels slippery.