I tried them and opted against them.

on the plus side:
- the cats do not mind them
- it does stop the damage from scratching


on the negative side
- they do not last as long as they say. They fall off one at a time and there always seems to be one to replace.
- the cats struggle more and more each time you put them on. (and I did not want the cats to become fearful of the nail clipping process)
- The cap can get caught on things, like strings on your heavy scratching posts. The cat cannot get loose because the string is looped behind a "lip" that is formed between the cap and the nail and the strings can be too tough to break. I had to rescue a 2 out of the 5 cats I had the caps on during my 2 month trial period