I have had the EDT5 for awhille now and really like it. I believe that the difference between the 3 and 5 is that the 5 will do both 2 and 4 strokes both single and twin cylinder. The 3 I believe is just for single cylinder 2 strokes. If I was to do it over I would have gone with the 3 being that it is less expensive and I only use it on saws.