Lots of comments on Facebook are very dismissive. Yes, the quality is not as good as native 4K, but my goodness it is close enough to be worth the performance increase.
Ever since DLSS was announced I have said that if fake 4K, faux-K if you will, is good enough that I can't spot the difference when the game is in motion then I will be more than happy with it assuming there is a decent performance increase.
The images I have shown on page 2 of this are pretty good examples, showing a 1080p shot (main menu on the RTX 2060) and the distant bridge in the Volga map at 4K (the image is 1 20th of a 4K screen).