I can't comment on the chairs other than to say that the double-slat is not a functional requirement. Harbin's design was informed by the type of chair found in London parks. (I used Harbin's chairs - his actual chairs - in another routine when I performed at the opening of the new Magic Circle Headquarters. They were larger, i.e. taller, than I had imagined.) I acutally have two different sets or style of chairs for my routine, depending on the nature of the show. So, the look of the chairs can and do differ. The key is how the anchor chair has been constructed, something you shouldn't be able to discern from a photograph. It is, afterall, supposed to looked exactly like the other chair.
Bill Smith, and others, use a more convention conference style or banquet style chair. In addition to calling Bill, as suggested by Bill Palmer, you should speak with the dealer offering the chairs. I find it hard to believe that he would advertise the product, and attach Bill Smith's name to item, if it wasn't the case.