I believe that spec sheet on the 250EXT is out of date. There were some problems with the first run of these that are just now getting sorted out. I know there were changes to the frequency and pulse rates, and other changes as well. I would inquire as to the most current specs sheet to compare. Also the 250EX is shipping now, where as the 250EXT is being tested and finalized. No idea how long that will take and when it will actually be shipping. Several features were dropped from the initial specs, such as different wave shapes, that changed the machine somewhat.