These have cropped up before, but I couldn't find any scale reference pics. Best info I could find is that, according to Kid_Kyoto in
this post, the base and first level (if you removed the smaller tower) have about a 10-model footprint.
Personally, I don't find them interesting or detailed enough to buy, since, as cheap as they are, I could still spend less and get a sheet of foamcore which, coupled with some free cardboard/-stock, could easily turn out two towers that looked just as good (or better, with some time and effort). For quick and dirty table fillers, though, you won't find anything cheaper and Michaels aren't hard to come by.