I found out something new yesterday, it appears that the Karoo Hammerhead bicycle computer is what I would call 99% Garmin Mount compatible. I say only 99% because they have oriented their mount the way Garmin did the old bike mount kit for their Forerunner watches, it is offset 90° from the Edge mount. But it is 100% compatible with my Garmin mounts since I redesigned my mounts from the very beginning to be Forerunner & Edge & Varia compatible. With an Eighth-turn mount you can mount in either portrait or landscape orientations using the exact same mount without modification.

So now I can claim Karoo compatibility, when using any of my Garmin mounts.

Here is DC Rainmaker's review of the device, https://www.dcrainmaker.com/2018/02/...th-review.html
It appears to be on sale at the moment for $349 USD with free shipping.

Note that I don't actually have a Karoo, just the mount insert (Which surprisingly can be ordered separately) and their pictures show a 90° offset in orientation of their mount, it might be able to mount without the offset, I simply have no way of knowing.