You really need to do some diligent research on two stroke oils if you have an issue using the Stihl oil.
There is a lot of bad info in this thread.
I have many two stroke high performance engines. Some in excess of 200hp coming from just two Pistons.
The oil I currently use is $10 per gallon on sale.
I have never ever had a damaged engine because of oil quality.
But you will be using so little oil, why not just use the Stihl stuff for the extra warranty? The amount of money you spend on oil for it will be small, whether it's Stihl oil or cheap stuff.
Once the warranty is up, use whatever you want.
Of course if you were handy with engines, you might not care about warranty.