I use these at loud gigs and also band rehearsals. They are very decent sounding, easy to use and quite comfortable.
They come with a detachable cord and a little case (when cord is attached you can put the plugs in a box and wear it on your neck when not used).
Before I got these I used earplugs with an earpiece that had to be mounted in ear, it was a bit annoying and storing wasn't as easy. After doing some research it seemed like the ER20s will be just fine and I'm quite happy with them.
They are not perfect but you would probably need to go custom made route and spend ten times more money to notice significant improvement in sound quality and comfort.
These are size S and they fit ok in my ears, I would say that my ears are standard/average size, perhaps a tiny bit towards small.
Overall they are good earplugs and I would recommend them but due to different ear and ear canal sizes this is very subjective. You may need to go through couple of different brands and sizes before you know what you need/like but these are perfect pair to start with.