I may get blasted for this, but....Ryobi does not make a tool (none) that will stand up to commercial use. Every other Saturday homeowner use, maybe.
Commercial quality trimmers are worth the money, both in their longevity and performance. There are many good brands to choose from: Tanaka, Shindiawa, Red Max, Kawasaki, Honda, Echo, Stihl. . .and more.
I know that Echo & Stihl both make power heads that you can interchange multiple other tools with. The Stihl line is the KM90, KM110, and KM130. I have been running the KM110 for 6 years commercially and have had 0.0 problems either with the engine or the interchange connection.
Ryobi makes some cool tools though. Many times I have walked by their display in HD and wish some other brand would make something they have. . .