The scrub plane is not so much as a particular plan design so much as a method of preparing and using a regular bench plane. The purpose of a scrub plane is to easily remove a lot of stock to either thickness a board or to remove surface irregularities such as cupping or twist.
A scrub plane is identified by the severe radius on the blade, typically about 75mm. This allows the plane to rapidly remove a lot of wood very fast. In the past timber framers would use a scrub plane to size timbers for sockets or joints. Also cabinet makes would use a scrub plane to size timers before finishing them with the jointer and smoother. Any bench plane (except perhaps a jointer) could be made into a scrub plane by simply shaping the blade with a sharp radius. In fact many hand tool woodworkers keep separate blades for a bench plane with a severe radius to use as a scrub.
Since the scrub is pretty much "brute force and ignorance" it does not need any of the refinements and sophistication of your regular bench plane so Veritas has produced a bare bones plane that has a very simple body a single securing screw and an iron radiused at 75mm. They call this the Veritas Scrub Plane.
The body is about the same length as a jack so it is ideal for flattening boards as well as thicknessing. My old bench consists of three planks of 50x200x2000 jarrah and the centre plank has about a 2-3mm cup. I used my new Veritas Scrub Plane to flatten out this cup before smoothing it in preparation for jointing the edges for a glue up.
The scrub plane was a dream to use and made very short work of the section in the photo to the right.
I had a chance to pick up this plane second hand for the price of a quality plane iron which saves having to reset the plane every time I want to use a scrub plane.
The Veritas scrub plane is simple easy to use and is an excellent addition to the hand tool workers kit.