It wasn't a success. In all, it looks like they only released a handful in the initial 2011 launch period, then didn't release any more.[1]
I had a copy of Cloud Atlas in flipback format, and it was... okay. I bought it in that format purely for the novelty of it. It felt a bit like reading off a pair of playing cards hinged together, but wasn't entirely unpleasant. Reading a fullsize paperback is nicer if you like the paper reading experience. The paper alone makes a difference; it's very thin and crinkly, like old onion skin paper, or the paper in a Bible, or the paper you buy to roll your own cigarettes.
The main advantage it has over a Kindle or Kobo is that the book itself folds down smaller -- a little bigger than an iPod Classic or a pack of cigarettes -- and it won't run out of battery power. In most other respects, the eReader has the advantage.
I don't know anyone else who's ever read one.
[1]: https://www.amazon.co.uk/s/ref=as_li_ss_tl?rh=n:266239,k:fli...