The market for the ebay item is (I think) derived from the poor rear seat belt configuration of many 'small' conversions. Having 3 seat belts up-front frees-up the options in the rear.
Obviously these handicaps don't impact current Calis.
Of course the design relies on having huge space behind the passenger seat to execute the turn. This isn't a problem on most conversions with a off side sliding door (hence units behind the driver) but wouldn't work with RHD Cali's with the units behind the passenger seat.