I disagree with you about the boxes being too restrictive.  They are the result of a great deal of testing.  The official Earthbox site has a section geared toward commercial growers.  In it are several pdf's that document the reduced costs and improved yields that the box produces.  

Our boxes have roughly the same dimensions, but are put together with readily available components and cost much less.  There are some trade-offs as I've mentioned at the Flickr link.  Again, we're not selling anything, we're giving it away.

Copied from the official site, here are a few of the benefits of using their system -

"*  Organic growing requires no three-year transition period;
      the first crop can be certified with OMRI-approved products.
    * Spring crops are ready up to two weeks earlier than in ground.
    * Fall crops have superior production for top-end market.
    * No fumigants are required.
    * Eliminate clean soil cultivation.
    * Eliminate erosion.
    * Produce two crops per season, without rotation.
    * No nitrates are released into the soil.
    * Use 60% less water.
    * Minimal herbicide required.
    * Use 28% less fertilizer.
    * Use 10% less insecticide.
    * Leave stakes in the ground year after year.
    * Spend 26% less on production with the EarthBox."