Hi, thanks both! So I dug around on those two devices, and it seemed a little hard to tell which was going to be better.
The camlink is seen by computer as "webcam", and therefore works with all software, eg skype/zoom, and is a tiny device.
The gamecapture HD60S+ works in OBS, but not in other apps directly, is larger, but has the benefit of monitoring what is being sent, and can use for streaming/recording other devices, like the game capture it's meant to be.
So I went for the HD60S+, as it seems a little more flexible, and I use the webcam feature of OBS anyway for things like teams and skype and other apps...
My canon allows you to turn off display, however I was still getting a record/pause dot. But then I found in the menu that you can turn of display capture for HDMI, and you get a completely clean feed.
Thanks again for all the help, very useful!