When shooting birds at relatively close distance with a long focal length, it is challenging to keep the entire head and bill in focus, and a narrow aperture is the solution. This lens is built for that specific solution, and bird photography is a good use for this lens.
The f/11 fixed aperture brings significant benefits, including light weight, compact size, and low price, and these features meet a range of other needs. Those not able to (or do not want to) carry heavy gear around, those not able to afford the expensive glass, beginners, kids, etc. are loving this lens and its 600mm sibling. These new RF lenses fill that niche.
The Canon EOS R5's animal eye AF performs incredibly well with this and other bird subjects.
While the f/11 max aperture reduces the camera's AF area (and pushes ISO settings up), there was no need to select a specific AF point to keep this little green heron's eye in focus within that area.
Simply frame and shoot.
The bird turned its head?
Frame and shoot.
A larger version of this image is available on Flickr.