Thinking of picking up two Stihl Kombi KM 110 units. One straight shaft trimmer head and another edger head. I plan on leaving the heads on the units most of the time. My thinking is, if I want to add the saw head or shrub trimming head later I can. If one unit goes down, I can just swap attachments until I get it fixed. So is my thinking good and is this unit a good choice?