My buddy is a square file pro, wish he had a computer. I was taught outside in too. Tried square file year's ago for a short time. Most of us here do it by hand, and round file. Alot of faller's though have bought chisel grinder's. One thing I rally feel, is a true square ground chisel chain, hand file'd or with a grinder, will do some serious cuttin, and fast. Round file'd probablly a strong second. I have thought about going back to the square file, and next time My buddy Brian is here from Oregon I am going to have him show me how he doe's it. He is a veteran faller, and he has a grinder now has for some years. If square filed true, the real corner will grab, and bite better in undercuts. Especially if you like me like the Humboldt. I have heard all argument's, and tried all chains ever made. Round, full comp, semi skip chisel, full skip chisel. I alwayl's wanted what I thought would be the best. True round chain is more forgiving, when dull square will lose a corner, and is done. But any chain will dull, and I take extreme measure's to keep them sharp, and out of the dirt. Even chip bark of tree's I fall with an ax sometime's. The fastest chain I have ever used is a true square ground full skip chisel. Smooth to most guy's who complain they vibrate either hit the raker's too much, and or dindn't measure or gauge em.
