I have found the Stihl (Pferd) 2 in 1 file guide to be the best out of all the devices I have tried (electric, manual, on the bar, off the bar). They have three sizes (need correct file size and pitch to match the saw). Vermeer/Sherrill has the one for .404 pitch. Depth gauges and cutter teeth get filed at the correct angles and height at the same time. Tool flips over to do both left and right cutters while the chain is on the bar. Files are replaceable. These are on all my trucks and I've labeled them for the different saws. My guys use them daily in the field.
http://www.stihlusa.com/products/chain-saws/accessories/filing-tools/2in1file/
Can you use any file with this device or do you have to buy specific files from Stihl?