Personally, I do use Focal but i find that it's only useful to a certain extent.
Firstly, for wide angle lenses you won't really need to do much AMFA..you really can't tell the different and the adjustment is done wide open…i doubt many will shoot a wide angle landscape type shot wide open anyways.
It works well for more" zoomed" lenses…for me 50mm and above. And i don't even think it works for zoom lenses that well since the 5D wil "average out the in betweens"
However, for specific lenses like 85mm or Macro lenses..it works fantastic..you do see a huge difference if your lens is out.
But, depending on the distance and lighting condition, Focal might give varying results so it's best to do the adjustment at the distance you USUALLY shoot at….