I have been using readerplates from readerplates.com on a sony prs505 for over a year and love them.  The subscription is 10 dollars a month for the entire US plus AFD.  You can’t ask for much cheaper than that.  They have an installer which will download and install them for you, directly onto the reader, or you can just download the large file and extract it onto an SD card.  Pop it into the reader and you are ready to go.  They just added the AFD to the approach plates as well, so you have a wealth or information for 10 bucks.  They also make the plates for the kindle, but having used touch screens before, with the Eflybook (waste of money), in a true IFR cockpit, working a stylus or the little kindle controller can become very frustrating.  Since these readers are slower to load, if you make the wrong selection it adds more heads downtime going back and forth.  The sony reader has line select buttons, much like a flight management system, and can quickly rotate and enlarge the plates.  Even though the screen is smaller, I find no problem getting the essential approach information off of the reader, without having to enlarge it.  I only enlarge it for large airport diagrams, but I also usually print those out at home ahead of time, so I don’t have to switch back and forth from the approach plate or departure procedure to airport diagram, when busy.  The battery lasts for ever and the case is aluminum and appears to be very robust, as most sony products I have owned are.  The eflybook was flimsy and had screen cracking problems, not to mention slow and 300 dollars a year for the subscription.  The eflybook included IFR enroute charts, but since the unit is soo slow, it is impossible to use the chart function.  I have also used the 2000 dollar electronic flight bags, with moving map gps and vfr charts.  They are great on the ground, but in an IFR cockpit, big, heavy, and the power drain is significant.  My biggest problem with them was the backlight at night or dusk would kill your night vision.  The sony readerbook, I select the approach I want and then throw the unit on the seat for reference when I need it, and keep the aircharts IFR low enroute book out under it.  These have been my experiences.  It may not be for everyone, but everyone I show it to and uses in actual flight, not just on the ground, see’s how the simplicity and ease of use make the sony not only the best deal going, but most helpful was to reduce cockpit clutter.  You can find the sony reader book for 230 to 280 dollars on ebay.  Brand new from sony for 280.