I can tell one thing though some of the 4 stroke string trimmers are a real pain to work on. I recently worked on a Ryobi RY34442. In order to change the timing belt you need to disassemble the half shaft crankshaft by pressing it apart. It is the same if you need the piston out. I was here lucky as I have a 12T press.
The engine ran very strong after the repair to only it come back a week later with a severe lost of power. It had blown an oil seal and had destroyed camshaft bearing surface. The only way to fix it to short block which cost nearly 2/3 of the retail price of the whole trimmer not counting labor. They even sell the need engine internal parts individually here.
Here in the US the four stroke trimmers just don't seem to hold up to the demand users put on them. Some user have great results but most users have nothing but nightmares.
