On the left is a traditional holdfast (it may well be the Gramercy, I can't remember), on the right is the Veritas holdfast.
The Veritas has a bit more reach, but the Gramercy has loads more grip and is much faster in use. Veritas also make some mini holdfasts like these,
They may have uses for say a vertical leg post or holding a jig, but I find the grip to be borderline inadequate and they're right faff to set up and use because there's very little travel to the threaded part.
One option instead of holdfasts is to design your bench with an open slot or with lift-out tool well sections. Then you can just drop in a whopping F Clamp and secure the job from the rear. This means there's no need for any holes in the bench, you can apply pressure to any point on the bench surface, and if you want to turn your bench into a quick veneer press you can load up with as many cramps as you need.
Then there's the old Marples style of holdfast, which are secured into a metal collar that's let into the bench. I never got on well with that style of holdfast when I used them years back (there was a time when they were pretty standard issue on British benches), the collar is generally in the wrong place for what you want and it can nick your chisels, plus the grip as best as I can remember was similar to the large Veritas holdfasts, ie okay-ish but not quite as much as you'd like.
My advise would be build a bench with a slot, failing that go for the Gramercy style. If you're unconvinced and want the Veritas large style then PM me and you can have two for the price of a single new one plus postage!
