I just bought some a couple days ago to replace my D'Addario fluorocarbon strings which had started to fray. I play a Kala KA-T tenor and use a low G string, as you might expect. I mostly use my ukulele like a miniature classical guitar, plucking the strings with my nails. I have nearly 20 years experience playing music, and I play my ukulele several hours a day, although I have only been playing the ukulele for a year. I only have experience with Aquila Nylgut and fluorocarbon strings. I stretched out the CarbonBlacks, and they stay in tune. I don't have a lot of knowledge with regard to strings, but I'll post a non-technical review here.
The strings had some interesting properties, but overall, I was very disappointed.
First I'll give a general description, then I'll summarize with a brief list of pros and cons
Aquila says the strings are their answer to fluorocarbon. I am not sure what that means; they feel different and play completely differently from fluorocarbon strings, although the CarbonBlacks do have good sustain like fluorocarbon. Most of my playing has been with fluorocarbon, and I'll focus on comparing these strings with fluorocarbon.
The strings have a soft, somewhat rubbery feel underneath my fingertips, and the low G string is wound. This is neither good nor bad, but the feeling is quite different from the hard plastic feel of fluorocarbon. I think most people would describe the tone as "warm." The pitch warbles more immediately after the strings are plucked, which is kind of nice, more guitar-like. The strings have a much lower tension than fluorocarbon strings, and feel denser. I think this is part of the reason why the CarbonBlacks allow me to play with a more even volume across the entire fretboard, which is a good thing. It is also easier to bend notes. However, it seems that the range in volume is less, and, more important, it is nearly impossible for me to play in tune, because if I apply any more than the slightest pressure to the strings, the pitch goes sharp. This is especially true higher up on the fretboard. The difference between a light touch and a heavy touch can be as much as a semitone. It sounds horrible. No guitar-family instrument will ever be completely in tune along the entire fretboard as long as the frets are straight, but for reasons I'm a bit too lazy to expound upon, compensating by bending, etc. is very difficult with these strings.
The expressiveness that is gained from evenness of volume across the fretboard and the ability to bend notes is obviated by the fact that in order to play notes at high volumes, it is necessary to press down harder on the strings to prevent the string from slipping out from under your fingers when plucking hard, which, as I noted above, throws the note off pitch.
A separate set of issues relates to the wound G string. I have the same problem with controlling the pitch as I mentioned above. The other problems I suppose aren't unique to this set of strings. The timbre and volume of the G string are different enough from the other strings that chords are dominated by the sound of the low G string. Plus, the harsh sound of my fingernail scraping against the winding is not nice.
Pros:
-Even tone across the fretboard
-Easy to bend notes
-Good sustain
Cons:
-Very unforgiving of changes in finger pressure
-Strings have inherently less range in volume
-Even if they did have greater range,
it is nearly impossible to play in tune at higher volumes
-scraping sound on the wound G string
-chords dominated by the sound of the G string
Neutral:
-Soft feel on the fingers
-Warm tone
-Low tension
I have tried to emphasize the good and bad points equally, but for me, the difficulty of controlling the pitch really overwhelms any of the other benefits of these strings, at least on my ukulele. I am sure that a more experienced player could keep their finger pressure at just the right amount to keep all the notes in tune, but he would still have to deal with the wound G string, and it is very difficult to control the pitch when fretting.
I ordered a new set of D'Addario fluorocarbons the day after the CarbonBlacks arrived.