Has anyone used this HEDS unit (optical encoder for DRO)

At the following site:

http://www.usdigital.com/products/h1h3/

There is a HEDS unit that I'm thinking of using for DRO and
feedback. I like this unit over the one at:

http://www.usdigital.com/products/s4/

because it has the option of a dual shaft allowing a inline
connection to a dial knob if I'd like.

Thanks,
Ken