Oops, calculated the surface area wrong.

29"x21"x21" is 29*84+2*21*21 = 3318 sq in = 23 sq ft
12"x6"x5" is 12*22+2*6*5 = 324 sq in = 2.2 sq ft

23 sq ft surface area for the regular oven, vs. 2.2 for the toaster oven.

I also use a shelftop electric oven about the size of a microwave (it
actually is a microwave too, but a 500W microwave is too underpowered
to be useful). That's as well insulated as my big oven, judging by
how warm it gets in use.

I do believe in sizing the cooker to the food. A fullsize oven to
roast 2 potatoes is wasteful.

Dave