The only ones that I work on that is under commercial use is the Husqvarna HU625HWT. The first one the customer didn't survive beyond the first year of use. The equipment failure was lack of maintenance, they never changed air filter and it so clogged mud that suck a hole through it which allow dirt into the engine.
Now to the things I have seen to happen to the two current trimmers the nursery has in use. The mow balls fails quite regularly due to dirt getting the ball bearing. The replacement belts Husqvarna sent out didn't fit; way too short. I had to modify the engagement assembly by moving the brake. This allowed me to install a standard inch size belt. This still had the head turning some in the disengaged position which has since stop. Next problem that required me getting a machine shop involved was the spindle shaft. It fits too loose in the bearings allowing it to slip instead turning the bearings and wear out the shaft journals. I had the shaft knurled for a press fit which resolved the problem. One other which was customer induce was the addition of fuel strainers as grass was clogging the carbs.
The customers personnel has since been trained to check the air filters and oil before which use. This resolved resolved the engine failures in general they were having with all their equipment. To give an idea how dirty the filters getting look at the filter in the following thread on the handheld Echo stringer trimmers after only one month of use. They had brought in two of them into the shop in this condition. I didn't even they had them so I got a filter short.
http://www.ppeten.com/forums/viewtopic.php?f=3&t=2447Considering the abuse they receive at the nursery they are holding up well for this particular customer on the 30+ acres that they maintain.
The truest measure of society is the how it treats its elderly, its pets, and its prisoners.