From what I've heard (but not experienced myself) the C.B is way more "rigid" than its competitors. For just that reason I bought one & the roti as well.
I can't say anything against the spitfire but the 2 C/B units stack even together & are solid rigid & very well made.
It also includes several "goodies" like the ring, dual grates & diffusion if thats any help.
You can also use the original grate raised up a little giving 2 complete "racks" to cook on, & add the Webber warming rack for another 1/3 rack.