I've taken two rides with the speedometer installed, and it seems to be working, except that it's having location-dependent problems acquiring a signal. Also, it's telling me I'm going slower than I think I am, like when it says 60 I feel like I'm doing 70. I guess the next step is to get paced by another vehicle.
This may not be the ideal location for the antenna (under the steering damper anchor plate). All I can glean from the documentation, which is just a few crude drawings and a bunch of Chinese writing, is that the antenna should be mounted horizontally, right side up. But perhaps it needs to be more exposed. I'll try it like this for a while, as the research continues.
Now I just need to paint the bracket and tidy up. I may paint the back of the gauge black, and remove the threaded studs that are for panel mounting. And I need to find a place to hide all that antenna wire, now coiled under the left handlebar (visible in first photo).