You don't need the spark arrestor to stihl tools at first, but it will make your job so much better. Although it isn't the same as driving without an air filter, it does help keep dirt and sawdust from being sucked back into the engine. Any dust or dirt that enters the piston may cause it to score.
My friend had a small mower shop where he sold all equipment and tools and also provided services. However, he was at a loss and decided to close the store. I have no idea what happened. Perhaps the pandemic situation is also a factor.