Royal Oak String Cleaner - Small

I had never used string cleaner before, but now I wouldn't be without it. The product works well at keeping excess rosin build-up off your strings. It makes a big difference on the string sound when all the rosin is removed! Highly recommend the Royal Oak String Cleaner

What is it? What's it do? How will it improve the sound? How do you use it?

This string cleaner is overall satisfactory. Has a faint soapy smell, but it doesn't feel soapy or waxy. What's nice is that the bottle comes with a small nozzle that prevents the contents from spilling out all at once. What was a little inconvenient was that it doesn't come on pre-moistened cloths, but that's probably only inconvenient for me because I've only used pre-moistened cloths in the past. It does remove build-up on strings fairly well. I would wait for it to dry completely (usually takes a couple of minutes tops) before playing again.

I have several students whose strings have heavy tarnish, so I was hopeful that this would help smoothen the coarseness of those strings, as well as remove the tarnish. (The strings were placed on the instrument by an orchestra teacher, who it appears
bought in bulk, and did not store properly to prevent tarnish). I'd say it's halfway effective. It smoothed the strings, which really was the most important. It also removed rosin buildup (which wasn't really my main issue, but still obviously important).
However, the string in question remains black :(