Those "DC servos" are closed loop steppers with the driver and encoder integrated into the motor, which is pretty neat. You just supply the DC power (48V or so) and the step/dir signals and it does the rest. These seem to be clones of the Leadshine Integrated Easy Servo family, although I've no idea how well they've been cloned. http://www.leadshine.com/producttype...stepper-motors

I used a 2Nm Leadshine on the Z axis of my Bridgeport conversion and it's been seamless. Having said that, I've only used proper AC servos since, the last lot being the Lichuan A4 servos that JAZZCNC has been using. They are a bit basic on the software front compared to a Yaskawa but seem to work adequately and are a fraction of the price. You can also swap the cooling fans for something more civilised easily enough if you don't want to have to wear ear defenders(!).