It would be better than free hand sharpening. I never have use the Stihl guide but I have use other guides for years with good results. I have however since a couple years ago gone the Oregon chain grinder. Mainly due the hardness of some chains that I was doing for my customers.
What is more important is consist sharpening angles which any file guide will help to provide. I get in free hand sharpen chains where some cutter are barely have angle and then other cutters have extreme angles all on the same chain.
If remember correctly Stihl chains are usually done at 25 degrees where Oregon chains are done at 30 degrees. Either angle is fine for cross cutting and occasional rip cut. But you done primary rip cuts then you want file at 10 degrees as you want the shavings to break up more so they will not clog up the saw.