"Lemon oil" is a misnomer too. It's almost never actually lemon oil pressed from actual lemon peels, which is very acidic and should not really be used on bare wood. I'd stay away from lemon furniture polish as well. It often has silicone oil in it, which can be a nightmare when it comes time to refret or refinish the neck. Good luck gluing frets or binding to a fretboard that has been saturated with silicone oil for years. Nothing sticks to that stuff and it can be a huge pain to remove as well. Steer clear of plant based oils too. Those go rancid over time.
No need to spend a fortune on fretboard treatments or cleaners. The primary ingredient in most of them is just plain old mineral oil and often a touch of lemon fragrance. Go to the pharmacy and buy a bottle of food grade white mineral oil for a couple of bucks. It's used as a laxative and is sold with antacids and other digestive medicines. No weird chemicals or fragrances, and you'll have enough for many years of fretboard oiling. Works great on cutting boards and wooden spoons and such as well since it's non-toxic and doesn't go rancid like plant based oils.