I started thinking about the kind of hand tool work i'd need to do right now and one example is a finished drawer box that fits tight...so i need to plane some off the side. That led me to ask "how would i hold this on my new bench" and i had a hard time imagining how to do this w/a leg vise and a wagon vise. So that led me to see the twin-screw as likely more usable.
That is one reason for having the top overhang some past the legs. Of course there are ways of attaching an "overhang" on the side of the bench with a thick board and a couple of holdfasts.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)