I've never had much success sharpening chains with a chainsaw file, possibly because I've only tried to use them after somebody has just accidentally hit a rock or a nail and blunted the teeth far beyond the point where a light touch-up with a hand file is going to do them much good. A few months ago wibble_puppy bought a Faithfull electric chainsaw sharpener; I tried it out on a totally blunt blade that wouldn't cut at all with limited success: afterwards the chain would cut in a straight line but quite slowly with a lot of dust and effort. I read a lot of reviews of different models before recommending the Faithfull machine so I was a bit disappointed with the mediocre results.
I'm currently processing a pile of sticks into firewood so I decided to have another try with the electric sharpener, this time experimenting with different settings and carefully examining the edges under magnification. With a bit of practice I managed to get the blade pretty much as sharp as a new one! I think the trouble the first time I used it was that the instructions supplied with the machine assumed you were using it to touch up a slightly dull blade; this blade needed considerably more grinding to get it back to a good set of edges. Hopefully the next time I'll get away with just giving it a light lick to restore it to full sharpness. My main complaint with the Faithfull machine is that the power switch feels a bit cheap and is awkwardly located.
It's a little thing, but I do so enjoy using sharp tools.