Well, that all looks good.
It’s interesting that the text is working, since it uses the exact same mechanism.
Have you tried changing the static values to get it to re-run the transform?
Have you tried viewing it in a browser?
Ignition version should not matter here.
I have tried changing the static text to have it rerun the transform. It cleared my manual change to the points value, but returned it to all the arrows sitting at the top.
It does work in the browser though!
Is that just a case of test with a browser open? Or is there a fix?
Maybe? I am on 8.1.35 and it works as expected in the designer. But occasionally there are things that don't fully work in the designer, but do in the browser. 
Testing with the browser open it shall be, until I can persuade the powers that be to update the version we have, and then I'll see if it works in the Designer at that point.
Which would be interesting!
Thanks again for putting this together 
Full stop. There are many things the designer cannot do (navigation, project-specific auth, docks, and more). You must test in real clients. (Both for Perspective and Vision.)