I had exactly what Allan is describing last night a 70's Tele with a 9th fret that was humped up in the middle not the ends. Kind of unusual and the fret was not loose and would not go down any further either with our press or a special tool Dave invented that uses a loaded spring from a punch to drive a fret down.
So the D and G strings had to have their action raised outside of the gentle progression of increasing action that I set the treble to bass side to. The thing was in for a set-up, it's a basket case with lots of other issues we were not to address (electronics and more) and this tool would have been perfect.
We normally and you've likely heard me say this before about normally addressing the fret plane as a whole as the strings see it and that would make any spot leveling tool not for us. We instead would recommend a proper fret dress with the idea in mind that this likely is not the only uppty fret and we can correct them all with a fret dress.
But when the budget for the player is not there and it's suitable for the instrument why not spot level and this tool looks cool for that.
Then I looked at the price
but still it looks like a good idea and I agree with Allan on when and where to use it.