I believe that the bottom line is this. If you start doing practice PFL's on roads then you run a very major risk of causing traffic chaos or even a bad accident, even if you only go down to 300ft. People driving won't know that you're only practicing.
If you pracice PFL's into a field then there's little or no risk of causing an accident with traffic on the ground. Anyway don't you do power fail landings in the circuit where you practice actually putting it down on the tarmac with idle power from 1000ft. When you do practice PFL's in the training area the main objective is to set up the glide, pick a good spot, note the wind, and then set yourself up so that you can establish yourself on finals into your chosen spot.
If you can do a PFL from the circuit and land safely and if you can get down to finals on a selected field/area in the training area, then in the unfortunate event of a real power failure you would be able to, or at least have a very good chance of putting the plane down in a selected safe spot whatever the selected safe spot happen to be.
Martin.