The only company at present making 21:9 panels is LG. So the LG 25UM65-P, Asus PB298Q, Asus MX299Q, AOC Q2963PM, and any 21:9 panel made prior to 2015 will use the exact same panel in each of them. The only difference will be the ergonomics, the case, the OSD and any OEM features added.
I would like to point out that I have had three of these monitors from dell, and unfortunately I've had to send all three back due to QA issues, possibly effected the whole batch. The first two had really bad clouding on the left hand side of the panel and light bleed in the top left corner and bottom left corner. The third one had no light bleed, but this one did have very bad IPS glow (considerably more than the first two), and was unable to display text as good as either of the first two panels.
I would like to add that if the first panel had the same amount of light bleed as my last panel, then I would have kept it. Unfortunately I purchased this panel to watch 21:9 movies, and the amount of light bleed made them unacceptable. I would have probably kept the third if it wasn't for the really poor text rendering.
Earlier on I said they use the same panels. Well, I purchased an Asus MX299Q, and I had that panel sat right next to this Dell Panel. And picture wise (apart from the flaws), there was no difference. I did checkerboard tests, colour tests, the lot.
I can only assume the differences you read on the review sites such as TFT central are purely down to the panel lottery dependant on the batch. Something to bear in mind, as you're probably better off going with the AOC version of this panel, as it's around £50 cheaper. I'm happy with my Asus Panel now, and I can't be bothered to send it back to try and save £50, when I could be back in the panel lottery again! No thanks.
Ergonomics : 5/5
Dell produce a wonderful stand, that allows you to raise the height of the display, and lower it so it's almost touching the desk. It swivels about 130 degrees left and right. It also has a USB3 hub, two around the back, and two on the side. The Dell stand is the main reason I chose this in the first place.
Build Quality: 4/5
I would have given 5 out of 5, but if not for the poor QA on my panels. Other the flaws previously mentioned (which may not bother you), the Dell is certainly built better than my Asus, it's a solid bit of kit, that can be used in an office, and could take a few knocks or rough handling.
Picture Quality: 4/5
The colours are accurate, there is very little banding. There is no black crush, meaning you can tell the difference between 1% grey, right down to absolute black. This was the same as the Asus panel, which is why I'd advise going for the AOC if money is tight. (It's the same panel). Homogeneity of 100% white wasn't as good as the Asus Panel, but that will purely be down manufacturing tolerances.
This panel does not use PWM (which my previous dell did, hence why I had to get rid), so you can turn the brightness up to 100 and down to 0, and you will not see any flickering at all. All the LG panels use no PWM. Thankfully. The screen coating is lovely, it's not harsh like on my previous dell, giving a matte effect. (Same as on the Asus)
The colours pop, and the contrast is great. Gaming is fantastic on this panel, no motion blur in the games I played.
If you can get a good panel, I recommend this one, due to the stand, the USB hub and the build quality. I would have kept mine if not for the issues I had.
Overall, it's a great monitor.
I simply cannot go back to a "normal" monitor after using 21:9.
Although I imagine I will be buying one of the 34" 1440p monitors once they come down in price.
Probably next year.
I hope you get a good panel if you like watching horror films or playing horror games.
These are great monitors.
Just a shame mine all had issues.