I went from Maseru to Matatiele via Ongeluks nek, fully loaded with tent and gear and only had to put in half my fuel capacity.
13 odd litres for just over 300Km of riding that day. Admittedly it was slow, easy riding.
It's a good investment for touring on the 690.
I picked mine up for around 5k second hand. New they well over 10k now.