The machine duly arrived after two days from order. It took half an hour to add oil and petrol and then we were ready to get going. The scarifier on the lower settings is quite fierce and I removed much of the dried/black moss and the grass in a short period of time on the back law. On the other two lawns, I used the second setting and, although it removed much of the black moss, it left quite a lot of grass. I know that I will have to use it right through the growing season.
I would recommend purchasing the 272litre dumper bags for the amount of moss removed. I took a dozen bags off each lawn down to the tip as I didn't want to use them as compost.
A well worth machine to purchase but do think through how you are going to handle the resultant moss as there will vast quantities left over.