Don't know anything about ben heasons slab panel, but mine is about two foot high and at about 70 degrees probably (total guess).
I would say that the specific angle is pretty irrelevant as the sloppiness of the holds will be your limiting factor if you see what I mean.
I use mine to train balance and footwork. Standing on it static, walking around on it and jumping onto it (all no handed obviously as it is only 2 foot high). Use small footholds. If it is easy to stand on just use a smaller slopier foothold. Use one of these and you will really see ahuge improvement in your footwork and your trust in your feet. You will develop a better 'feel' for whether your feet will stick or not.
NOTE: Make sure the board is well secured before you try any jumping onto it antics!
I seem to remember agreeing to write a feature about making and using a footboard for Bubba, maybe one day I'll actually do it?
