I was interested in the 200-800 also. I already have the 100-500, which is just fantastic. Christopher Frost just put out a video on the 200-800 and I was a little disappointed with his results/tests. Seems it's pretty soft, especially at 800mm. But for the price still very decent.
I just received my 200-800. The funniest thing about it was that it was packed in a box the size of what an L lens would typically be, inside a carrying case. But since it isn't an L, and doesn't come with a carrying case, there was a cardboard box inside the cardboard box

It included a kind of useless strap, but (yay) a lens hood. It's about the same weight as a 28-70 (though of course much longer), and the two can share 95mm filters. The ergonomics are good, but I miss a separate control ring + focus ring like the 100-500 has. The control/focus ring is also not clicky, obviously.
It was pretty cloudy when it came yesterday, and I haven't done much with it, but I snapped the photo below handheld in my back yard at 800mm, at 1/800 f/9 ISO 6400 on an R5. It's literally the only photo I took - I had only a couple of minutes. Pixel peeping, it doesn't look tack sharp at 800mm, but obviously, some of that's could be me.
I also own the 100-500. I don't think that it's an either/or. I do not like the 100-500 with a 1.4x extender (because of the protrusion at/reduction of minimum zoom). The autofocus on the 200-800 is very fast (and very usable); impressive, in my opinion, given the aperture.
In the grand scheme of things, I think I'm pretty happy owning/keeping both, though the overlap means I'd rarely, if ever, pack both with me.
