I planted a couple rows of them in one of my gardens a couple years ago.
I bought the BOSS from a bulk barrel at Big R. The stalks grew to about 4.5 - 5 feet tall, most had three flowers. Not huge, the seed area in the middle of each flower was only three or four inches across.
Same year I grew mammoth grey striped sunflowers. Those stalks all got to ne around 9 foot tall and most seed heads were 12-15 inches across.