Behind the sack extender?

I just got myself a Penimaster Pro few weeks ago. Was wondering if it is safe to extend with base behind the ball sack? Has anyone tried it before? Will it cut off circulation to balls easily?

I found it is not safe and puts too much pressure on the perineum nerves. Ball burn is in my opinion the number 1 thing that will destroy your extending time and there is no way around it.

+1 is not very comfortable around the scrot, I wear it at base of penis and sometimes use foam or such on the base, which isnt really necessary just provides extra comfort