My monitor is HDR 400 which is one of the lower end HDR versions and I tend to have it on rather than disabled as I do find in games mostly it's better visuals, in driving games and open world panoramas etc.
It can be a bit off putting sometimes though when it gets confused and the screen will dim or brighten up on the fly...
...but thats mostly only obvious when I'm watching say a movie on VLC, the control bar is quite light so it will make it think to darken the screen overall. Until the control bar auto hides itself and you can see it brighten up again!
Hdr400 is quite bad in of itself but it is useable in some instances like a very bright racing gamenl like forza or something. The main issue just hat hdr400 screens don't have enough dimming zones and when the hdr kicks in to make the bright colors pop it raises the brightness of the blacks too and so any black areas of the image look completely grey or like it's covered in mist.
The biggest issue with raising the brightness of the blacks is that it reduces color contrast and the human eye perceives color contrast as both image resolution and image quality - meaning you can trick the human eye into thinking an image is of a higher quality and resolution than it actually is by improving color contrast - and the exact opposite applies, poor color contrast on an hdr screen can make the image appear worse to our eyes than just using sdr
Linus tech tips did a video comparing various hdr monitors using the movie how to train your dragon and its shows off what I'm referring to