Paul, I ordered the new Byrnes variable speed 4 inch sander as soon as it was available. Like all Byrnes tools it is a wonderful, precision machine. In my opinion, there is one caveat. It is a little under powered. At least from my perspective, is more of a finishing sander. When I pressed a 1"x 1"x 2" piece of pear stock it would reduce the RPM. This was not with a significant amount of pressure. I had a couple of phone calls with Donna, Jim's wife to be sure that this was by design. She conferred with Jim and stated it was. She offered to exchange it for the original non variable speed 5" sander, but I decided to stick with it. I actually didn't require variable speed, nor being able to reverse the motor and disc direction. I bought it for future scalability. I believe the VS 4" has a 90volt motor. While the original 5" sander uses a 1/3 HP motor.
The only other challenge I found was the lack of independent sources of 4" self adhesive sanding discs. Could find tons of hook-n-loop, but self adhesive not so much. McMasters had some available, at a premium.
I do love the machine. It will just take a bit more time for some jobs. I would make one suggestion. If you don't require variable speeds or to run the disc in reverse, I would go with the original. It has all of the other abilities to sand complex angles and with much more power.
Let me know if you have any questions on it.