All I can add to this is that the Progressive Dynamics unit I have is built
like a tank.  Looks and feels like the engineers designed it to work and
hold up and no production engineers or MBAs got in their way and said "We
can make most of this out of cheap plastic in China".  And their Website
actually provides easy to find, easy to read technical information and very
little hype, something that gets more rare all the time.  An example is
Surepower.  Their Website used to contain tech specs, wiring diagrams, and
installation instructions.  No more,  Now a pretty Website with little tech
info and a lot of hype on their products.