questions on cheap DRO

I'm upgrading from the mill on my HF44142 3-in-1 to a new mill/drill
from industrial hobbies (30x/12y/5z travel), and want to put DRO on
the new mill and maybe also later on the lathe part of the HF44142.

I like the documentation/feature set for the Shumatech DRO-350, but am
not sure I'll need that much power, as I draw nearly everything I
machine out in CAD, and can fairly easily have it print absolute
coordinates around whatever point(s) of interest I choose.

The 3-axis display that SMW sells on eBay looks fairly primitive
(toggle/inch metric, zero each axis), but I'm wondering if it wouldn't
be enough and if not, couldn't I always just upgrade the display part
of it later to a DRO-350 (and maybe keep that somewhat limited SMW
display for the lathe which I use less often/precisely than the mill).

Pricing difference between SMW chinese scale kit and DRO-350 with
chinese scales (also from SMW) currently looks something like:

SMW on eBay Shumatech
Display & Cables 430 225
32" X Scale incl 192
12" Y Scale incl 44
5-6" Z Scale incl 40
Shipping 8 8
Total 438 509

A few questions:

1. Can anyone comment on the question of functionality? I can see
how the additional functionality of the DRO-350s firmware would be
useful if you didn't have dimensioned CAD drawings available, but is
it worth an additional $70 and the hassle of assembling the DRO-350
from parts if you have proper drawings?

2. Does anyone know if the cables that SMW provides in their ebay kit
are plug and play compatible with the connectors used on the DRO-350
or if I upgrade later, would I have to buy/build new cables?

3. Also, is there someone that sells just the glass scales? I don't
need the extra precision for anything I'm doing now, but have been
reading alot about homebrew EDM stuff which at somepoint I might like
to fool around with. If it only cost $100 or so more to upgrade to
glass scales with the DRO-350, I'd have to seriously consider it just
so I'd have them.

4. Are there any other cheap DRO solutions I don't know about that
work well?

Thoughts, opinions???