I have one as well. Its great! The delay isn't so bad. It is more than when receiving video through my goggles. Quantitatively, not sure how much the lag is. I'm sure it depends heavily on the specs of the pc it is connected to, and the application that is rendering the video. Like you said, maybe in race conditions the lag may be too much, but it is more than adequate for everything else.
It is also very convenient for things like tweaking OSD layouts, or troubleshooting hardware, but also great as a groundstation and spectator feed... It would be nice to integrate it into GCS, but imagine it may be hard to manage the delicate (in terms of latency) "live" stream in addition to everything else GCS already does, especially if you're also doing telemetry.
Bonus - some smart tvs will read and display the feed with no additional hardware or cables.