As well as a possible durability issue there is a weight issue with the 4 stroke line trimmers, AVB. A reasonable number of contractors use the Honda trimmers here, and seem to be quite happy with them. Others complain about the weight and price, but I haven't yet heard any reports of unreliability, with the Honda.
From this long, long distance I think perhaps the lousy performance of many 4 stroke trimmers and catalyst-equipped 2 stroke trimmers reflects the relatively short time since low emissions became mandatory. I seem to recall something similar happened when outboard motors were forced to have oil-free exhaust and low emissions, but with the outboards, the problems were overcome fairly quickly. My guess is that the same will happen with the trimmers. Meanwhile we in Australia will sit back and watch you guys suffer the pain so that we can share the gain once the new technology is properly developed.
