I also just got some stylast... comments on the performance of stylast welcomed!
I think use of the LAST products that 'preserve' requires a bit of a leap of faith...as you
most often do not have a test album or cartridge that is exactly the same and has been untreated (tho BaMorin's testimony above is noteworthy)
Those that 'clean' take less faith - you either hear it's affects or you don't. Fairly straightforward there.
Joe Fritsch, was the former Chief Engineer at
Allsop (known for audio/video cleaning products) and inventor of the Allsop cassette head cleaner AND de-magnetizer (those of you old enough probably had one or both of these items about)
He left in the early/mid-80's to form his own company based in Ireland, called
Trackmate. I'm not sure if Trackmate is around anymore, but until the past couple years, they sold cleaning products worldwide and was an OEM to Radio Shack in the US for many years. The mechanical parts of their cleaners were terrific and they bought chemicals from the likes of Kodak (CD/DD lens cleaning solutions), Dupont, etc. Impressive list they hung with

I met him several times in the mid-80's and he told me succinctly that LAST Products did
exactly what they say they do. He tried, repeatedly, to buy their products to pair with his mechanical cleaners to no avail. The owner of LAST goes his own way and does not share the technology with anyone.
I recently had really my first occurrence in 20+ years where I realized that StyLAST really
did work.
A
Denon DL160vdH I had bought sounded terrible. It continued to sound terrible many dozens of hours into playback - normally more than enough to flesh out the character of any cartridge so I can judge it. This one was perplexing - as it sounded HORRIBLE still - and it was a cartridge near universally lauded for sound qualities.
Well, I realized somewhere along the line that I was treated it to StyLAST every 2 sides (the norm, for me) like I do with all my (old) cartridges. Once I stopped applying it and let the stylus shape wear in for another 50 hours the cartridge came alive - it's among my favorite cartridges now. The StyLAST apparently was so capable of stopping stylus wear in its tracks that it wouldn't wear in. I now use as it's fully worn in.
So, based on that, it seems StyLAST really works. Prior to that freak happening I was, literally, taking it on faith of Joe Fritsch that it worked.
btw, I have the same ~$35 bottle I bought 25 years ago and it's only half-empty now. So, one bottle could last a lifetime so its extremely inexpensive protection for your pricey styli.
John