What I don't get is the following from the ad copy:
"All the Brewbuilt kettles follow the recent trend to a 1.2:1 ratio where the height is 1.2 times the diameter. This is a proven commercial ratio that has been adopted in homebrewing to achieve a more consistent 10% evaporation rate during the boil. We do like this ratio for boiling. For Mashing we would prefer a little bit shallower but that is a small compromise. Dimensions for a hot-liquor tank, if you are thinking brewing system down the road, are irrelevant as any ratio kettle will do."
On Northern Brewer they talk about how it's "scientifically" determined. All of it is complete nonsense.
If you're using a gas burner the most important specification is the diameter of the pot (all else being equal) that mostly determines how much energy is transferred, the ratio has little bearing on the boil-off rate.