We have used one of these for about ten years with great success.  The tractor can even follow the hose around gentle 10' radius curves.  The little ramp clips on the hose and has a folding ground spike to keep it  from slipping.  When the tractor reaches the ramp, it pushes a shut off  valve on the belly of the tractor.  Very simple and effective.  Part of our  ramp finally snapped off, but it still works.  We've never had a problem  with the tractor.  The adjstable spray wands allow you to regulate the size  of the area covered.  I suppose it can drag about forty feet of hose before  it slows it down.  That probably will vary depending on the depth and  density of your turf and how straight the path is.