Hmmmmm, really? I can do an 18" chain in under 5 minutes fee hand filing in the field without taking it off the saw well enough to get surprised compliments from folks watching me work.
There is always someone who will be faster and better. The Granberg and Oregon bar-mounted file guides are very good for getting consistent angles. They are good for developing filing skills and confidence, and for periodically correcting some of the variation that hand filing (especially free hand filing) will produce. They have been around for a long time.
Welcome to A.S. Homelite410
Philbert