The Tessive shutter system differs dramatically in both function and effect from a mechanical shutter, but it's understandable that this question would arise. After all, judder in pans and motion generally looked more fluid in film cameras, which obviously had a mechanical shutter. So why did things get worse in digital cameras, and how is the Tessive system different?
To understand the difference, we first need to look at how a mechanical shutter is different from the electronic "shutter" on most digital cameras.
In film cameras or digital cameras with a mechanical shutter, the waveform is approximating a square wave, but due to the separation of the shutter disk from the sensor or film, there's a bit of a shadow blur on the edge of the shutter. This means the transition from closed to open and back to closed will have some smoothness to it. With an electronic shutter, there's almost no rolloff at all, as the individual pixels transition almost instantaneously. In the graph, you can see this slight smoothing of the mechanical shutter. This corresponds to the slightly softer look produced by mechanical shutters. In the same graph, you can see the exposure waveform of the Tessive shutter.
So it's reasonable to say that there is not an enormous difference between an electronic 180-degree shutter and a mechanical 180-degree shutter from a waveform standpoint. A mechanical shutter can be useful for correcting rolling-shutter artifacts in digital cameras, and also allows for a reflex mirror for an optical viewfinder. But often it's the motion look that drives the desire for a mechanical shutter, and this motion look difference is very minor. The Tessive shutter does a much better job of correcting the look of motion in-camera.
For examples, we used a Sony F65 with a mechanical shutter. The same pan was shot with the onboard electronic, mechanical, and Tessive shutters. The following images compare these shutter modes. These images were acquired by Tim Kang, who conducted this test of shuttering modes.
In the first image, the pan rate was about 17 degrees per second. In the full-resolution insets, you can see there is only a very slight difference between the electronic and mechanical 180-degree shutter, while the Tessive shutter has dramatically smoother motion. In the case of the fence, the vertical lines seen in the moving images are aliasing artifacts, and actually end up moving the wrong way.
The next image is the F65 again, this time doing a whip pan of the same scene. This shows the effect of the shutter in a more dramatic motion, and again both 180-degree shutters have similar responses, while the Tessive shutter has a very different look.