I have two machinist vises that I use on the mini mill. Zero lift! Well not quite zero but less than my Wilton drill press vise conversion. A little different to operate but they are rock solid. I made some dedicated table clamps for these vises so they could be placed very close together or far apart on the table. I use a parallel to align the second vise to the first when ever it is needed for large work. Now I can hold much larger pieces on the mini mill with the vises.
I normally only tram in the first vise on the right and then let the parallel do its work for the second vise. I like to set the first vise on the right side of the table and then reference anything else to that. Allows me to mount and use the rotary table and not have to remove the main vise. If you are going to use this type of setup it would be best to buy both vises at the same time and they should be identical. Mine are not so I need a small spacer to bring the short one up to the height of the high one.