Thank you all for the replies.
Thank you Neil for the engineering explanation, was enlightening......had thought the 'box' shape would be easier to build but apparently not!
Realise that car, trolley or tunnel kilns would be very different as they are usually used in high volume, architectural or industrial type applications and other than some raku kilns I have not seen gas fired 'bucket' ones.
My curiousity was mostly about the 2 designs for comparable size kilns.....the kilns as was said, that go into homes, basements, small/ medium size studio situations or into teaching environments.
It appears that manufacturing costs and the consquential retail price are the main reason for the top loading preference in the US, which is ironic because our front loaders are about 25-30% more expensive than a comparable top loader here yet we seem to prefer front loaders anyway!
I have 2 front loaders in my studio. I also have 2 small portable kilns that fire from our Australian 240V/10amp domestic plugs that I take with me in the car....hey!! painters have portable easels for location work.....I have a portable kilns!........(use them to test found clay deposits while on holidays)
The hexagonal one is great for tumble-stack bisque firing or a few small things for glaze but it does seem to me to be less space efficient for glaze firings than my portable 'box' kiln so found the 'debate' between Mart and Claypple interesting........thanks Mart for the diagram!! (I really am a visual learner).
jrgpots....have just seen the 2 part open bucket design you mentioned on our main manufacturers site, it's called a 'split tube' furnace...... new to me!!!