What really matters is that you find a method that works for YOU.
I do disaster response, where the trees are filled with dirt, and metal, and all kinds of stuff. On a bad day, we can go through a dozen chains in a half hour, and run up to 17 saws, so we keep an Oregon 511 clone in our equipment trailer and run it off of a generator.
Some people own just one chain that never leaves their saw, and cut firewood with it for years.
I recommend that operators carry 3 chains per saw, so that they can swap out for a sharp chain and get back to work if they hit a rock or just get dull. They can concentrate on sharpening back in the shop, instead of in the woods, and there is less temptation to cut 'just one more log' with a dull chain.
For field 'touch-ups', a file with a guide works fine.
For regular sharpening, a good electric grinder has many advantages over a using only a file:
- it is much faster if you have many chains to sharpen;
- it is better for grinding back a chipped or damaged chain;
- it is consistent: all the teeth are ground at the same angles, which means that the chain runs and cuts smoother;
- (ibid): all of the teeth are ground to the same length;
- the wheel constantly exposes sharp grit as it wears - that is, you never find yourself sharpening with a dull file that someone should have replaced;
- the fine grit leaves a very smooth finish and sharp edge on the cutter;
- there is no chance of 'rounding over' the cutting edge at the last instant by moving the file imperceptably.
It is possible to grind the life out of a chain by hogging off lots of metal, or by jamming the wheel into the cutters until they turn blue, however, it is also possible to just 'kiss' the dull edges with a feather touch and hone them to a razor's edge that is a pleasure to use.
The 'on-the-bar' guides or grinders can be OK if you are a 'one-chain' kind of guy (male or female), but you have to stop work each time. Also, don't forget to flip your bar over each time you sharpen, regardless if the same chain remains on the saw, or your bar will wear unevenly.
The Dremel tool, and it's 12-volt cousins can also work for you, if you feel comfortable with them. I get a little concerned that the diameter of the stones change as they wear, which affects the size and shape of the gullet on the cutting tooth.
If you do file by hand, or use one of the Dremel-type tools, I recommend that you have it ground on an electric wheel-type grinder every 3rd or 4th sharpening to get all of the teeth back to the same size and angles.