Fully-manual lens means fully-manual shooting. Although the camera would meter everything, since it doesn't know the aperture, you might as well just ignore it.
This was the first time I'd shot manual focus in like 15 years, and I feel like I borked a lot of the shots because I didn't get a split focus screen for the camera, but, still, the amount and quality of light that hits the sensor through that gorgeous German glass made me really, really happy. I've had the lens for about 15 years (and the R4 it was attached to), but only last month did I have the presence of mind to figure out what adapter I'd need to put it on the 5D. Wish I'd done it three years ago.