To determine the effectiveness of this technique vs. another strategy would require accurate measure to assess the impulse of the jump(s); something difficult to measure without the right technology. I think you can get a good visual idea of it, but obviously this is subjective.
The pretension theory makes sense in working to develop and increase foot/ankle stiffness and elasticity, especially as it relates to sprinting, just prior to the support phase, where this foot/ankle position is commonly found (although this is questionable for some sprinters). The idea with the pretension, I presume, is minimal ground contact time with maximal rate of force development. Simon Hunt's video below is nice demonstration of the ankle position and the reactivity of the rebound in these types of depth jumps.
The excerpt below is from Jim Radcliffe and Robert Farentinos's "High Powered Plyometrics". In this case the 'pogo' would be a learning exercise for the jumps, and the specific technique involves the pretension position: "upon takeoff, the ankle must lock the foot into toes-up position (dorsiflexion), maintaining this locked position throughout to ensure sturdy contacts and quick, elastic takeoffs."
The Maasai people of Kenya and part of Tanzania, are well-known for the adumu, a dance ritual of repeated jumps, attempting to jump as high as possible. I would be very interested in what sorts of impulses they create and heights of jumps they can attain. To me they seem to get pretty good heights with good elastic rebounds... without the same dorsiflexed position as taught in some plyometrics.
So does this mean that the dorsiflexed position is flawed, or could the Massai be more reactive if they adopted a more dorsiflexed ankle upon jumping? Or, do the Maasai possess better innate capabilities to modulate stiffness at the appropriate times?