This was terrible on my fish & chips the other night, although my palate felt pretty fresh and zesty afterwards.
After that disappointment I thought I'd try it on my new Ibanez Talman guitar that still smells of fish (it came out of the box that way, as the bishop said...). It did a lot to improve the odour of the guitar even though my playing still stinks. I don't think I'll try it on my hands though.
More importantly it helped a lot when cleaning the rather well-used neck of my 1980 Stratocaster, which came up a treat and looks pretty nice now, just how I remembered it, but with a zesty lemon freshness that makes it feel like playing in an Italian orchard.
I shouldn't have to tell anybody how to use it but, for those guitarists unused to basic household chores (99%?) I will. Put a bit on the neck, preferably with the strings off, covering about 5 frets at a time, and rub it to cover the fretboard in that area, thoroughly, with a non-abrasive cloth (especially on finished necks!), as though you're trying to grind it into the wood. Then leave it for just a few minutes (maybe five) to do its magic before wiping as much of it off as you're able. Really try hard not to leave any residue anywhere, especially along the frets. It's a finishing layer on the wood, not a deep wood treatment, and the frets go deep into the neck, so clean it off really well before moving on, use an old toothbrush if you must. As you move up the neck you might be tempted to do more frets since they're closer together. I tend to avoid this since I'm concerned about keeping the oil around the frets for as short a time as I feel I can get away with, so I do smaller areas with the same number of frets as I go on, using less oil each time and working hard to keep the fret-fingerboard area as clear as can be. Don't work so hard that you remove everything, just bring the fretboard back to a clean state, easily eyeballed. You can cut down on the times if you use this more regularly. If you have the discipline to do this as a weekly job, you can be very quick and sparing on the oil, I would guess, because it is more maintenance than restoration!
For really grubby fretboards this oil should work pretty well, although I read some advice online about using Windex or other cleaning compounds in moderation, and leaving them on the neck for minimal time before coming in with the lemon oil and finishing the job. Lemon oil is better for the wood than solvents and other compounds would be.