Activate all Karbon tool in your kritarc (not needed, But I've checked it works with them too).
Launch krita
Create a new document
Create a new vector layer (the unit spinbox is used essentially for Karbon tools for the moment).
You can try the freehand path and draw path karbon tool, set a size in any unit you want and start to draw.
Then you can use the default tool (moving, resizing objects, setting a shadow). In all thoses steps you can use units like mm, cm, pt, ... but also px, vw, vh).
Finally open the add shape and shape propeties docker. Add a few shapes and try to change the properties. deselect the shape reselect if, you'll found that the unit is reset to px (the spin box has been destroyed, then recreated).
(I had a lots of problem with this docker, it needs a few refactoring to work with the new spinboxes).
Close krita and check there's not segfault caused by the patch (I had this problem a few time, and had to find way to prevent it).