It is not a scam however there are some caveats. The machine is only as good as the operator. Also the machine just levels. It doesn't do any fine detail work. Nor does it do the fret ends, which sometimes need help. They say you can really fine tune your bass or guitar with a PLEK and if you traditionally use the same type of strings and setup they can supposedly dial in your PLEK and really customize it.
For me though, most of the time you don't need a complete fret level, you need a competent tech to diagnose whichever frets are problematic and level those and then go through and crown and polish the rest of the frets. Is it worth the money? It depends. If you can do it locally, it's probably about the same as a tech will charge, maybe a bit more if your tech is inexpensive. If you need to ship it somewhere, you can add in another hundred bucks or so on top of the PLEK price.
For the cost of one PLEK though you can literally buy the tools to do this yourself. A couple youtube videos and you can get this done on every bass you own for the rest of your life. It is an investment and it is scary the first time you do it, but once you get the hang of it, it's not hard. It is time consuming to do it right though. I generally had my basses out a week while doing fret level and crown work. A lot of times I'd also take that time to shield the bass, swap out any electronics I wanted, and polish the board and the bass.
