I am using three of these fingerpicks with a plastic thumbpick to play an acoustic steel string guitar.
Although I prefer the feel and control of using bare fingers on strings, there are times when I need brighter tone and more volume. These guys do the job.
Yes, they feel incredibly awkward at first and there are moments of frustration initially. But I found it well worth the effort. After a week or so of practice I was comfortable with them and they have definitely expanded my tonal options.
It may seem impossible to avoid the loud metallic attack and scratching sounds, but my technique naturally adapted to ameliorate these 'artifacts'.
It also helps to rotate them slightly so that the face is directly hitting the strings rather than the edge. Just be sure to wear them the right way round! Patience and experimentation are the key to success.
I can't see myself using any other fingerpicks now. They are easy to fit are comfortable for long periods of play, and will never wear out.