When I built my new bench, I built it in a way where it would work well with many types of traditional and modern work holding devices. Specially when it came to the use of the holdfast and the F-clamp. Now, as you can see from the picture, the Bessey F-clamp that I have is just about the same size as the holdfast I use. This was done on purpose, and it was also why I chose to build a split top bench.
Like many tools, everything has its strengths and weaknesses. The strength of the holdfast is its holding power and its speed of use. The only down side is if you don't have a hole where you need a holdfast you are stuck.
For the F-clamp, you can just about clamp anywhere, but it does take more time, and sometimes that means reaching under the bench to tighten or looses the clamp.
Both have their place and are well worth having in the shop. If you up in the air about having a holdfast then I suggest getting some of these Bessey clamps. Because you can never have to many clamps.
You can get them through the link about, it takes you right there. Or look at the other Bessey clamps they have at Woodcraft by clicking on the link on the right side of the screen.