I've got myself a shot of the neighboring farmer's chainsaw (actually he has several) to cut a couple of my trees down. However I've volunteered to sharpen them in future to save him the routine cost of the guy he's always used up till now. Ebay has a bunch of saw sharpening tools but every saw seems to be a different tooth size. 4mm, 5mm etc.
Is a universal tool a better idea than a set of diamond rasps for each size? What's my best option?