I agree with you completely, and at this point I think we will just use the two-way binding on the demo and combine the current two demos into one. That will happen for our next release, though. I am attaching the WIP version (it has not passed QA yet, and changing the selection mode at runtime is not a scenario we envision to be common).
In the meantime, the documentation provides 6-7 other examples for selection.
UI for Blazor