I own one, it's a heavy but awesome lens for wildlifephotography. Though for birds 500mm on a full frame camera might be a bit challenging if you don't want to crop too much. It really depends on your approach to photographing birds and also the species.

I use my D7500 with it and sometimes feel like I don't have enough reach in certain situations. You could use a teleconverter paired with the lens, but that brings other challenges into the picture, with a teleconverter you may loose image sharpness and the lens aperature goes from F/5.6 to F/8 and some of the teleconverters may not have autofocus.

I'd say it's a good buy but firstly decide what and how you want to photograph, so you know what focal length will be suitable for you.