Im sure poulan/ryobi/sears or echo will not fit a stihl.
My dad has a ryobi. Motorwise is fine. While it saves you money and storage space, it is pretty heavy relative to individual.
Also, i tried his hedge trimmer attachment - it is alot heavier than my homelite hedge trimmer. Lastly, the blower is lacking.

I have a KM 90. I bought it specifically because my old Ryobi hedge trimmer attachment grenaded and I wanted something that would stand up better. I run the Stihl articulating hedge trimmer with the carbon fiber extension shaft as needed.

My old Ryobi cultivator and line trimmer fit and work reasonably well with the Stihl powerhead. The OD on the attachments fit perfectly with the ID on the motor. Thedrive cable engages and works just fine. That said, as budget permits I will replace my older attachments with Stihl equivalents. I keep my line trimmer on my 2-stroke Ryobi head, but the cultivator always goes on the Stihl now.

The Stihl has tons more torque than the Ryobi - I had every intention of getting a 130 or 110 but the 90 was in stock and I haven't been disappointed in the last two years. Good Luck.