Its a £2700 lens. At that price I suspect anyone buying it can come to their own conclusions. Still on a full frame camera it is an extremely useful lens. The width makes it great for urban architecture, larger items in museums, and interiors in general. The short minimum focus distance makes it great for objects in cases and the lens’s sharpness makes it viable to crop the resulting images.
Obviously if you want to shoot longer than 24mm then you need another lens but for wide angle work the lens is excellent.
Downsides. Its a £2700 lens. You could buy quite a lot of other gear for that. The Sigma 12-24mm f/4 is about £1000 cheaper and nearly as sharp at the wide end. If you are shooting on a crop sensor then the 10-18mm is under £300 so unless you really really need the sharpness for some reason I wouldn’t go near this lens for a crop system. On top of that its big and its heavy. Not something I have an issue with but for anyone more weight conscious (but then why shoot full frame?) it may present a problem. The f/4 speed may be less than idea for indoor work but thats becoming less and less of a problem as camera low light abilities improve.
Overall a very useful bit of kit but also really rather on the expensive side.