I've bought nothing but used machines for my entire shop. The only unit I
got took on was a surface grinder. It looked great sitting there, but I
couldn't get any decent finish with it at all.

I finally bough another (used) one and gave away this unit.

Hydraulic feed automates the grinding process, indexes the stone across the
surface to be ground. Saves tons of time hand feeding. Think of it as a
powerfeed for the grinder. Normally an expensive addition to a surface
grinder.

My advice, this is one machine you've got to see parts run on it before
purchase.

Karl