Im looking at a new 3 m power Harrow , we have plenty of stones so which Harrow is the best on stoney soil. I'm thinking Amazon or Kuhn or Pottinger, I have two pottingers already but they changed their one piece tine to two single tines and a new adaptor plate for the older models , but it keeps breaking bolts and is not a good job. Are the new pottinger with their quick fit tines a success. So of the three which is the best.