a square reactor would work just as fine. just a little bit more work.. also more joints to worry about failing and of course the look, but it would be alot more easier to work with,,, as for the 1/4 inch thickness versus a 1/8 inch... the 1/8 inch is very brittle and cracks under the tinest amount of stress, whereas the 1/4 is a little more forgiving. This is very apparent where the tubing attaches to the curved surface of the tube.. plus the difference in price is only $25 - $30 more