Personally I'm not a fan of it. Even in transit, I often have a backpack with me and can read the paperback books I have just fine.
Plus, what's a better replacement to me, is just having the kindle app installed on your phone. When I don't have a paperback with me, I just open the kindle app and read from there.
Which arguable is even easier to carry for being in-transit than a small book, since people usually have their phones weith them.