OX with 90 Degree worm reducer for NEMA 23's question

I've been following the OX forums for a while now getting ready to start building one myself, and while I really like the concept, I am wondering about the resolution these machines are capable of. I was thinking of looking at ball-screw or rack-and-pinion setups for the X- and Y- axis, but this looks to add considerable cost - especially for me here in NZ the shipping costs alone become prohibitive.
I like the simplicity of the belt drive system (and the double belt setup looks like a...

OX with 90 Degree worm reducer for NEMA 23's question