Based upon many recommends on the forum, I've recently acquired a Virb Ultra 30. Unfortunately, there doesn't seem to be a strong community for these units. It does seem as though there's quite a few people here using them (including JG). Hopefully this thread can serve as a place where we can all come together and share best practices.
As for my experience, the plan is to record Auto-X runs and track days. I have a RAM roll bar mount to record hand position and track. Will be adding a second camera to a RAM suction cup mount on the roof. I'm looking to pick up the "powered mount" kit for inside the car, and running the external off of battery power.
When mounting the camera externally, I've been using basic cable tethers that are clipped into these mounts: https://www.amazon.com/gp/product/B07CTD41Y8
They're fairly strong (neo magnets) and have yet to give me an issue. I much prefer this style to looping around a mirror or similar.
As for my videos themselves, they leave a lot to be desired. After 20+ solo runs, I've only gotten one "complete" recording. For whatever reason, the video seems to clip right around the one minute mark. Additionally, the GPS data seems to lag about 20 second behind the video. I'm thinking the MicroSD card which was included (purchased used) simply does not have the write speed to keep up. Garmin seems to have a "recommended card" list, but that seems to be a few years out of date.
I will say, however, that when everything works, it works very well.