I like it. The books are good quality, with a range of styles/topics- DD1 enjoyed reading them. I liked the fact that you could choose just the phonics based schemes. It was great to have a constant stream of books at a suitable level, without having to search the library.
That said, I didn't use it for very long- just a few months, by which time DD1 had progressed so well that she could read most age-appropriate library books. I'm not a fan of reading scheme books once they get to the higher levels as I think 'real' books are more interesting.
We signed up for reading chest just before summer hols, my DD loves the sticker she gets for each book read, we made a big deal today about posting the ones read back, just waiting on the next lot to be delivered. Yes you can go to the library, which we will do as well for the summer reading challenge, I have a DS who is beyond the levels of RC, but our library does not always have a great selection of early reading books, also school broke up last week and we have yet to get to the library as we have been enjoying the nice weather, at least with the Reading Chest you just change books by popping in the post. I only plan on doing it until Sept and restarting again in the longer school hols.