I like the HF unit pretty well. A "light touch" works best. Once things are set, just touch the tooth for about 1 second. Repeat a couple of times if the tooth has obvious damage. The chains I use seem to cut about as good as they ever did coming back from the hardware store service that I used a few times for sharpening. I think there have been some reviews on the HF or CE unit, as well as the more expensive ones. It is not a high quality tool, but it seems to work pretty well for $29.
Hand filing like this only removes very little material and you'll get a long service life from your chains. I found brand new chains out of the box with a difference of .010 between cutter lengths. I like to keep them within 0- .003 difference between cutter lengths.