In the past, many people bought Canon lenses for their Blackmagic, RED, even some Panasonic
and (with mount converter) Sony cameras.
Failing to open the mount led to Blackmagic switching to L-Mount on their latest cameras,
and RED likely to phase out Canon mounts after being bought by Nikon.
Sony users with a bunch of Canon lenses were only one body away from switching back.
Canon is fast losing these feeder constellations.
That said, I love both the Sigma 1.4/50mm and 1.8/135mm ART lenses. The main difference
to their RF competitors is that I can use them on my BMPCC as well, and that the mount
converter with drop-in filter mount gives me black mist (from Meike), V-ND and C-PL filters.
One small filter for all my EF compatible lenses.
Aside of that these two ART lenses came with next to no chromatic aberrations wide open (!)
when Canon still was fast asleep at the wheel.