
Hi Bo'sun,
I also have a WM16B so for once I can speak with some form of qualification. 
The quill "DRO" is nice but it turns itself off and in doing so forgets where it is, so all moves have to be relative, this is a big deal compared to a real DRO which is continuous and allows clever functions.
The worm drive on the quill is lovely, so its not a big deal, but I shall be fitting a Z–axis to match my factory installed X & Y as time allows.
It has been pointed out that a "proper" DRO on the quill connected to work with the main axis DRO is a good thing, the electrics seem a bit expensive but I see the logic. It would allow use of the fine-feed on the quill rather than the courser Z-axis for small adjustments whilst still maintaining continuous accurate read out.