We have 6 or 7 of them at work. like the versatility of the unit. we mostly use the weedeater and straight hedge trimmer attachment. I believe most of ours are km94r. We have had a couple of the 100 level engines over the years and i can't tell a difference in power or longevity/durability.
issues I see with them as i have to fix them all the time. The drive shafts are the weak point. If you don't seat the attachment all the way in, the unit will still run but eventually round out the drive shaft of the attachment and you will have to replace. Easy replacement but also easy to prevent. Secondly the drive shaft to the motor can/will wear out the connection at the clutch due to poor seating. Through heavy use the seat and stuff loosen up which allow the drive shaft to walk its way out of the clutch seat which again rounds it out and renders the unit inoperable. You can fix it by putting a new clutch drum on the motor head which i do a good bit through the season. It is not fun to do though. Kind of a pain to get the split ring retainer off.
Long story short, they are great for the versatility and for homeowner type use they should hold up a long time. For more commercial type use, it works but be prepared for the maintenance described above.
I’ve been running the largest, KM 130 I believe, for several years homeowner use. I do make sure I drop the attachment in until it bottoms good and tighten it down good but I have not had any issues with it so far. I also run ethanol free stabilized fuel. I will say it’s somewhat of a heavy unit but I’m kind of a slight fella not used to lots of manual labor. Notice the weight particularly when edging. I’ve never once felt like I needed any more power out of it, no bogging down. I like the simplicity of only one powerhead, but if it goes down I’ve lost the use of three tools. I like the fact that the one unit is being run regularly whereas with the pole saw for instance, it might sit up for quite a while between uses which would likely necessitate either draining the fuel or other measures to keep it from gumming up. I use the trimmer, edger, and the pole saw, which saw a good deal of use this past week. I agree that they’re pretty ridiculously expensive. Buying just one attachment is about like buying a standalone unit. My neighbor owns the smaller unit and it seems to be working just fine for him.