First, is the eccentric placement of the rod. With the rod off center it creates a much larger reference area which makes the gauge more stable while in use. That is a major improvement in my book over all other wheel gauges. Also, all the rods are interchangeable between versions.
The second improvement is simply that the face is larger then the original gauge, but not as large as the mortise gauge they make. The larger area combined with the off center placement of the beam makes the reference area and stability even better.
The third major improvement is the material that was used. The stainless steel stands up a lot better then the original surface material and it weighs just enough to feel even better in your hand. The original gauge weighs 5 1/2 oz, Stainless at 8 oz , and the mortise at 9 3/8 oz.
In short, I highly recommend the new Stainless-Steel marking gauge by Veritas. With all the improvements over the original gauge and the fact that they are only available for a limited time. You really need to purchase one of these before they run out. I bought three, because I wanted more gauges and I wanted to replace my original gauge regardless. I also think that the stainless version will last a lot longer than any other gauge on the market and you can't beat the $29.95 price.
You can get the new gauges here at Lee Valley Veritas for $29.95