I just got done with 3 ten hour days on a stihl weedeater. I use the head that I load precut 8 inch pieces. A speedloader would not last a day with me!
Is this the line head you are using for your Stihl?
https://www.stihlusa.com/products/trimmers-and-brushcutters/trimmer-heads-and-blades/durocut/