You asked
Is the sigma bf good for video?
The Sigma BF page doesn't cover its video features, so I can't say whether it's good for video. It has no stabilisation in the body, so you'd need stabilised lenses for steady handheld footage. The page also doesn't mention a flip-out screen or a microphone input, and I'd check both before buying.
If you're thinking of vlogging, the video guide suggests a wide lens, around 16-20mm full-frame equivalent. These fit that range and are on the BF's lens list:
Written by Claude from this site's pages.