What is it , Stihl FG2?
If it is/was cheap good for You.
Give it a try , will require some getting used to though!
I have two filing guides similar to that one.
One is a Oregon and the other a no-name that came bundled with an supermarket electric chainsaw.
I got them both for free a long time ago.
Mine are quite flimsy , but they are great to equalize the length and angle of all cutters both sides.
I also sometimes use it to trim the rakers.
I still prefer free hand filing , but I use a guide whenever I notice my chains start cutting in a curve.
I also have a chain grinder , but I use it even less often then the guides.