First of all I had a swivelling Vertical Slide. Then because of its limitations bought a Rodney Milling Attachment for the ML7
Disliking the lack of rigidity in the foregoing two, I bought a Mill/Drill (The choice was made for me by the space and headroom available at the time, or would have bought something larger! )
Now with a larger lathe, I have, and VERY occasionally use, the heftiest Vertical Slide that I could find. It needed a slight adaptation to fit to the lathe, but has been invaluable for certain jobs that could not fit under the Mill/Drill.
But am under no illusions that it is stiffer than a proper Mill.
Horses for courses.
Howard