My understanding on this one is that they are basing the new inline spindles off of the SS machines. Better? Yes. No more belt and pulleys to wear out. Less heat since there is no belt rubbing on pulleys. Better surface finishes, again because the motor is coupled directly to the end of the spindle, there is no vibration from the cog belt running on the pulleys.
Overall, a good setup, (now that we got ours fixed, THANK YOU!). As far as how the 3 spindles differ, that is a good question. Maybe one of the techs on here will know.