It was the first time using such a product. It was absolutely excellent in cleaning both old and new strings.
I used it almost daily after playing (usually a couple of hours/day) and it kept the strings very clean and shiny as long as I used it. The shape and size is ideal, one or two swipes to apply on the strings and it is very practical to carry in a gigbag (flat and wide). It provides a nice slickness to the strings, just be careful not to overdo it. Mine lasted about 40 days, I wish it would last longer. To be fair, I think I used too much of it during each application for the first couple of weeks and perhaps it wasn't necessary to apply so often.
In a nutshell, it is perfect except maybe for the duration. I tried in parallel with the d'Andrea string cleaner, which cleans well but gave me a "sticky" feel to the fingers. I even tried to refill the Speed Slick with the d'Andrea cleaner so I could take advantage of the convenient packaging and applicator but that resulted in leaking. Next I will try the classic GHS fast fret and if necessary I will update this review.