I found almost no local retailer who carried this item although they did carry the type with the frame attached at both ends of the blade, and after trying to use it I think I may know why.  I was quite willing to sharpen the tool, and did so three times in slightly different ways.  Although it had a very sharp edge I most often could not make it cut well.  Performance seemed to depend upon what I was trying to cut; with just the right vegetation it did well.  But more often than not it did not do well. I tested it by trying to cut the vegetation growing in roadside ditches which was mixed, but all tender shoots, not hard, woody stems.  I did my best to find a proper technique and never did.  It may have been my fault, but the tool did not work well for me as I hoped to use it.