I have had a luthier tell me the same thing and then watch him use lemon oil on Rosewood and Ebony so I guess he is inadvertently saying you could use lemon oil as Fast Fret.
I LOVE GHS Fast Fret!!!!!!

I've been using it for, what 30+ years? Says right on the can 'white mineral oil'. (They use 'food grade' mineral oil on kitchen wooden tools, like cutting boards and wooden spoons.) When they 1st sold it, it came in a metal can, then they went to a thin plastic container that would break and the applicator would dry out.

Now they went back to the metal can.
I've never had a fret lift or loosen on any of my guitars, ever.
Blues/Jazz guys (Chuck Berry too), do a lot of slides from 1 note to another, slurs if you will, over a few frets. They don't always bend to the next note. The slur has a different sound. Fast fret is a great help to enable an easy, smooth slide. If you get the slightest sticking of your fingers on the string, the sound is wrong. It has to be as smooth as a slide guitar to get the 'slur' sound.
I
DO NOT drowned the strings with it, just a little. I put it on all the way from the head nut to the bridge.
I prefer rosewood fret boards and have always used
boiled linseed oil on them. Boiled linseed oil has a drying agent in it,
don't use raw linseed oil it will take forever to dry out enough so you can play.
I put some on
every time I change my strings. Again, I
DO NOT drowned it. I also use it on the saddle on acoustics, but I only apply linseed oil to the wood bridge a couple of times a year. I even use a Q tip to put some oil in the saddle string pin holes.
And I've been using good old 'Lemon Pledge' for polishing my guitars since the 1st 1 I bought. Go ahead and laugh but I love it.
Using these 3 products makes for very easy movement up and down the neck for me.
I had a friend (he past away) who refused to take an old tooth brush to the sides of his guitars frets to clean off the build up of crud. He said it would cause the fret board wood to rot.
When I was playing a lot (3 to 4+ hours a day, 4/5/6 days a week) in the summer time, 90+ degrees/high humidity, I would
KILL a new set of acoustic strings (GHS .012's, phosphor bronze, I tried .013's a few times but they were too much for me to handle) in a single ~3 hour night.
On my electrics (GHS Boomers, .010, with .011 swapped in for the high E and .014 swapped in for the B), under same conditions, took about a week.