"most importantly, when the ‘goodness’ from the ground has been used up and the ground has been well and truly pecked over by the hens, the house can be moved to a fresh paddock"

Found more examples of free range.

 "Being mobile the hen-house can be towed from site to site. The advantages of this are two-fold: first, the droppings can be cleared away. Secondly, and most importantly, when the ‘goodness’ from the ground has been used up and the ground has been well and truly pecked over by the hens, the house can be moved to a fresh paddock. This ensures there is no land contamination. This procedure also prevents the spread of any disease or sickness in the flock being passed on through cross contamination."

This sounds good, that they are mobile, but not until the "‘goodness’ from the ground has been used up and the ground has been well and truly pecked over by the hens". It will take a season or more for ground to recover and normally needs to be cultivated and reseeded.

I am not sure this is really any better than a static house for the hens or the land.

   

This seems to be a before and after pic..............

 

Source:

 at http://www.blackacrefarmeggs.com/farmlife/producers