Using a holdfast is not for everyone. Some people just don't like drilling holes in their bench, and others just don't find them as useful or very flexible. The best alternative and most flexible substitute that I have found are these Bessey Tradesman Professional bar clamps, which you can find by clicking on the link below. I chose the clamps specifically because of their throat size, clamping capacity, and strength.
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.
The reach of the two are very similar, with the holdfast having a 7 1/2" reach to the center of the pad, and the clamp having a 5 1/2" inch reach to the center of its pad. I should also mention that the pads on these clamps are larger than most at 1 1/2" round. You can also see that the clamps can reach nearly to the middle of each slab, providing them the ability to clamp something down just about anywhere on the surface of the bench.
That is where the flexibility comes in. With the split top bench I literally can clamp something down anywhere on the bench. This comes in really handy when shaping small parts over the edge of the bench, clamping pieces of a project down to the surface while working on them, or simply holding accessories down on the bench.
In this scenario I show three different ways I can hold a board down for work. The first and third are practically identical, and a perfect way for chopping mortises. Though the middle version may not be the best way for hand mortising, it would work find for trimming a tenon shoulder, or adjusting a dovetail joint.
And when it comes to accessories, here is a shot of a baton being held in place for use while hand planing. This is an area of flexibility that is hard to have with holdfasts.
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.