Ergonomic advantages over two displays are obvious. But it's hard to find serious FCP X users evaluate using a curved monitor for editing. Anyone using one? Does the distortion from the curve mess up getting graphics to line up or working with the horizon?

The larger the monitor the further away it should be from your normal seating position to reduce color distortion. A curved monitor might work but I’ve not heard of graphic professionals using them. You should research if these are recommended for pro photographers or illustrators who have very exacting standards. I think these types of monitors are more for entertainment purposes than work but who knows they could work well.

Yup. Been researching. Found the most conversation on REDDIT. Some people use them. Lots of theories on the science. Most pulled out of thin air. Hence the question here.

Seems like the monitor market for editing is driven a lot by laptop users not workstation users as in:
"Dual Displays" equals laptop plus big screen.

Three display edit suits wouldn't use curved so they get dissed fast. But for twin display environments, it's attractive. At least for me.

My twin Cinema HD setup is 32:10 with 3840x1200 resolution spread over 43".

Current 43" displays on the market are 16:9 which is crane-the-neck super tall. These are basically 4K TV's.

The largest flat computer monitors are 21:9 with 3440x1440 spread over 34". So you lose significant left to right space for productivity and everything is just that much smaller on screen (insert aging whine here). If I were on a laptop, this is what I'd get.

The closest I can find to twin HD monitors in a single monitor solution is 21:9 with 3840x1600 spread over 38". This is the closest to what I currently have. However all of them are curved (some only slightly but others much more).

Twin NECs or BenQ are always an option ... still looking.

My son in law has a big curved monitor but he is a hardcore gamer so I think those screens are very popular amongst the gaming community?

I use a 43 inch LG 4K Monitor (43UD79) and I had a 29 inch 21:9 monitor and a regular 22 inch as second monitor before, not going back anymore, love the size of the screen and I also use a second TV that gives me full screen preview from the timeline with a Intensity pro 4K card.

True. Many are driven by gaming features but there's a few models targeted at non-gaming productivity environments. My twin HD monitors are not and never have been oriented in a straight line side by side; always a slight V shape which is exactly what the curved monitors mimick. I'd hate to go back to the old days of one big monitor and one small one ... differing vertical resolutions and vertically sized panels ... ugh... that was so 15 years ago. :-)

Yeah, the 34" market is very gamer oriented and low price. LG produced a 38" panel last summer that they and a couple other companies created products out of. Dell as it turns out focused not on gaming features like FreeSync or high frame rates. Instead they focused on color and brightness for the office and home office.

Viewsonic, LG, Acer and ASUS each have their own variant but only the Dell specs 350 nits and at least markets the color specs. Can't tell if they actually did anything the others didn't.

I do a ton of graphic overlays and animation. Still gotta figure out how the curve plays out. And those Dell badges have to GO. Just gonna leave this here to see what everyone thinks:
https://www.anandtech.com/show/11653/dells-ultrasharp-u3818dw-available-curved-3840x1600

The spec I would judge first is this one: "Color Saturation 99% sRGB - 78.1% DCI-P3".
The Dell's 78% P3 is a little off to me. The LG I described earlier is "DCI-P3 99%". Start with monitors that are 99% 709A and work up to 99% DCI-P3. Better to have accurate color then think about the curve.

Yes, Toms Hardware has good technical reviews. Couple folks at Creative Cow were using these curved monitors just fine. After researching, I felt the 34" flat were appealing but not big enough to replace the twins. I looked at the 38" ... about the same as the V twins. They are all based on the same LG panel and have similar color performance. I went with the Dell U3818DW.
https://www.tomshardware.com/reviews/dell-u3818dw-curved-monitor,5282-2.html

The LG, ACER and ASUS were gamer oriented whilst the Dell and HP for professional environments. Can't stand the shiny white back on the LG.