You are under the assumption that the two are the same beast. They most definitely are not!!!
The Cornerstone kit you have is a klunker that far too many report on the various forums causes major headaches. First, the pit is not round, so the bridge binds partway through a rotation. The bearing at the bottom of the bridge pivot doesn't fit in many cases and that causes the bridge to wobble fiercely. Getting the motor (another $30) to mesh properly on the wobbly ring gear is a third headache. A fourth is getting the copper wipers to stay aligned with the two brass power rings that are slid up the bridge pivoting shaft. One or both will slip over time.
The one you see for $240, plus or minus, is a gem that you should sell one of your daughters for. Okay, that's a bit over the top...sell your wife, instead.
It works exactly as described, is easy, reliable, and if you can install it so that it looks like it belongs, it will be one of several showpieces on your layout. Operating it is fun, too.
-Crandell
