What resolution does it produce? My Sony α6100 yields only 1024×576, which is not great, though still better than any laptop webcam at 1920×1080, or mostly even a phone or tablet front-facing camera at 1920×1080.
(The Sony α6100 is also quite happy to run on USB power indefinitely, no fancy battery arrangement needed. I’ve used it thus for multi-hour webcam sessions, and plugged into a wall charger for multi-hour recordings, where its battery would otherwise be depleted after about 100 minutes.)
Another thing to be aware of when using fancy cameras like this is the latency: you’ll get added latency of 100–400ms, which is easily into the disconcerting zone if audio and video are out of sync by that much, so you may need to do things like add a corresponding delay on the audio, if that’s connected to the computer directly (which will give much lower latency). OBS Studio can do this. I don’t yet have an HDMI capture card, so I’m not certain about it, but the impression I’ve received is that latency will be much lower with a decent capture card than the USB/PTP approach, though still probably higher than your webcam.
I'm not actually sure what resolution gets passed through the USB cable. I would assume it's either native resolution or at least 1080. But to be fair I'm mostly recording in 720p 50fps, since the 4k is cropped with the EOS R and I felt more fps is better for webcam footage (the other modes are capped at 30fps (25?) or have a crop). Besides, people don't need to see my face in more detail.
I haven't seen any noticeable delay in the footage so far, but now that you mention it, I'll definitely keep an eye on that.
The EOS R can draw some power from USB, but it doesn't seem to be nearly enough, or it doesn't work while recording or something.
(The Sony α6100 is also quite happy to run on USB power indefinitely, no fancy battery arrangement needed. I’ve used it thus for multi-hour webcam sessions, and plugged into a wall charger for multi-hour recordings, where its battery would otherwise be depleted after about 100 minutes.)
Another thing to be aware of when using fancy cameras like this is the latency: you’ll get added latency of 100–400ms, which is easily into the disconcerting zone if audio and video are out of sync by that much, so you may need to do things like add a corresponding delay on the audio, if that’s connected to the computer directly (which will give much lower latency). OBS Studio can do this. I don’t yet have an HDMI capture card, so I’m not certain about it, but the impression I’ve received is that latency will be much lower with a decent capture card than the USB/PTP approach, though still probably higher than your webcam.