As I mentioned earlier, I don't yet have experience with USC as I'm still awaiting my Degritter USC.
But if you want to hear a comparison before and after an old record was cleaned, Degritter recorded such a comparison. If you go to the Degritter site here:
http://degritter.com/
You'll see a link just down a bit under "News," to the recording of a polish singer, where you can listen to the before and after recordings.Not all the crackle is gone, but there is an impressive (to me) clearing up of the sound, especially instrument tonality. Before sounds flat and whitened with noise. After at least sounds like hearing more realistic voice/instruments through some noise.
Of course grains of salt must be taken as this recording is offered by the company selling the record cleaner.
I'm still going to temper my expectations. For one thing a pal with a nitty gritty cleaner cleaned some old records of mine. They looked spanking new afterwards, but didn't really sound that much more free of noise. Similarly, I just received a 1979 record (bought on discogs) advertised as near mint. It sure looked near mint - either unplayed or having been put through a record cleaner. But it actually played as one of the noisiest records in my collection - tons of pops and ticks, and background noise (that did abate somewhat in to the recording).
So I'm learning you can't necessarily tell how noisy a record is going to be just by how clean it looks.
(And I'm also appalled at how visually dirty many new vinyl pressings are when I open them!)