Is it possible to transfer images from iPhone to SD card directly?
From my own testing, I have verified that unfortunately, you can only use the SD card reader with the iPad. You can also only transfer photos/videos from the SD card to the iPad, not the other way around. I think these would be great features (take it from a 8GB iPhone 5c owner) to have, but unfortunately they are not available at this time.

You can send feedback to Apple at http://www.apple.com/feedback/iphone.html as I have.

Edit: Now you can use the Lightning to SD Card adapter with the iPhone if you update to iOS 9.2! However, you can still only import from the SD card to the iOS Device and not from iOS Device to SD card. They have even updated the item description to mention iPhones at http://www.apple.com/ca/shop/product/MJYT2AM/A/lightning-to-sd-card-camera-reader. Still not sure about iPod touch (don't have one).