Lead Screws

Does anyone have any experience with the lead screws found in the
Small parts Inc. (pg 185) catalog? They look a lot like ball screws
and claim accuracy of .0006 per inch and repeatability of 50
millionths. They list a heavy duty anti-backlash nut also, it is made
of Polyacetal, which I presume is some type of plastic. The screws
are only $69.00 for 1/2" by 24", the nut is also $69.00
The 1/2" is the largest diameter they list and they imply lengths
over 24" can be ordered.
They may be a little light for a mill or mill/drill, but might
work well for a router setup or a sherline sized mill????
Terry May