It does work just like a rescue figure eight. I think it should have the capacity to work as a preventer as well. In its current configuration it neither works like a vang or a preventer, just a brake, so you still need both a vang and preventer as well.
Finally, it is ugly.
There is a tide in the affairs of men,
Which, taken at the flood, leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
Shakespeare, Julius Caesar IV, iii, 217