Should the vise be mounted flush with the apron, or with a spacer? This is a topic that are discussed from time to time, so I’ll give my stack of dimes on the subject.
Holdfasts are the rats in the shop whack-a-mole game. The frustration getter-ridder-offer. To be serious: they do one thing superbly well, and they are named accordingly. They hold. They are fast.
I saw a British gentleman flailing a hand plane at some wood propped up against a tree. Some episodes later, he had a work bench. Well, giddyup! I thought to myself.