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.
Flailing a plane about can be very rewarding or make the piece of wood look more like a cat’s scratch board. It comes down to whether the thing stays in place or not. Hence a planing stop. I bought one from Veritas, and tested if it wood stop the would. Or.. something.