I bought one for my iPad mini. The actual Apple reader and it didn't work. Something about formatting and the ipad mini would read the card...
Somewhat mad about that... I don't ever know what I did with the reader now...
Sooo to make up for that I went out and bought a very small Acer netbook for under $200 it works extremely well. I just carry it in my backpack and pop it out at each camera, move all the pics over to a folder and pop the card back in the camera. In and out of the woods very quickly!
There is not a sd reader for any iphone. if they advertise that it works on an iphone they are lying. The iphone does not have the software to use a sd reader.
As for ipads they can use sd readers. some cheap china ones may have issues but they generally work. on my ipad 2 i used to use a cheap one from amazon and it worked well until i updated my ipad. After the update it would not work at all unless i jailbroke my ipad and installed some software tweaks. then i went ahead and bought a new one from amazon and it work without a jailbreak.
My ipad always said that it was not supported but it would still work. I have read that the apple ones transfer pictures faster but i have not spent the money for a apple one.
If you get one off of amazon please make sure it will work with you ios on your ipad.