I have my Canon lenses from when I was shooting with my 550d. They are high quality L-series lenses, which were also a reason why I chose the Blackmagic. They work flawlessly. But also all compatible lenses from other manufacturers, like Tamron, Sigma, ... can be used without any problems.
The Blackmagic does not have a tracking autofocus, as is common today with DSLR cameras. You have to focus by pressing the autofocus button before you start recording and this setting remains unchanged during the entire video recording. Only a manual correction directly on the lens is possible during recording.
Contrary to my expectations, the Blackmagic is also suitable as a DSLR replacement for photography. It actually behaves very similarly to my 550d. I.e. you have to press the focus button before releasing the shutter (with the 550d you had to press the shutter button halfway) and the camera focuses. The prerequisite is, of course, that the lens has built-in autofocus. Images are recorded in 6k resolution (approx. 21 MP). Of course, you can also extract still images in 6K resolution from a 6k video using DaVinci Resolve or another editing programme. Since the recording is done in Braw, the images are almost lossless.
One limitation is the lack of a viewfinder. As a replacement, I bought a viewfinder from Kinotehnik, which is placed on the screen and provides a brilliant viewfinder image in 2x magnification.