The new $29 Reader has been updated to support the USB 3 transfer speeds of the iPad Pro. The Reader will also work with the iPhone 6s, iPad Air 2, iPad mini 4, and older Lightning-equipped iOS devices—but on these devices, transfer speeds are limited to USB 2 speeds, which is also the limit of the old Lightning to SD Card Reader.
Want to buy the new Reader? Keep an eye on the model number, which is MJYT2AM/A. (If you shop at the online Apple Store, the model number is in the URL.) The old version of the Reader doesn’t seem to be available on the online Apple Store, but it may be still in stock at other retailers. The old reader’s model number is MD822ZM/A; if you see it, avoid it.