Each brand of lemon oil is formulated differently. It all boils down to mineral oil, maybe some actual lemon oil, lemon scent, and varying amounts solvents or other stuff. Since it's not a food product, manufacturers aren't required to list the contents and ingredients so you never truly know for certain what a certain brand of lemon oil contains.Now I'm confused. I'm not a luthier, but I am watching this thread because I'm interested in the topic. How can lemon oil be rubbish and recommended by Alembic at the same time? Maybe it depends on the brand of lemon oil? What does Alembic recommend, specifically?
The thing though is there is no real consensus on the "best" oil for a fret board. Most of all you read on the internet about this stuff is a big load of "he said she said". You'll find just as many people and articles that are pro-mineral oil as there are against mineral oil. I just go on try things and make my own decision.
I concluded that Fret Dr is a slightly reformulated and repackaged bore oil. Bore oil is a mix of various tree and seed oils used to condition wooden bored instruments, which undergo much more moisture stress than fretboards. Like lemon oil, bore oil is simply an oil mix that is suitable for oiling bores, the specific formulas can vary between manufacturers. I figured if bore oil is used to protect unfinished wood from tons of spit, moisture, and humidity, it'd fair well for unfinished fret boards as well.