The solution I have now actually with this little box found for little money. The other features I've seen yet unspecified me. You have for my purpose initially load the Hama-app, or you decide to access via a browser on the data reader. Then you also have full access to the folder structure. Then turn data reader, if necessary, for example, to charge to a USB power supply beforehand. Then one is completely independent in terms of power supply. It now takes about 30 seconds until a LED indicates that the wireless data reader is built. Now connect to the iPhone settings with this Wi-Fi, and you're done.
Once the SD card from the camera in the data reader plugged in, and you open the app, you have access to the images. Now you can save the photos on the iPhone and needed to work with it further. The data on the SD card are not affected, so you put them just back in the camera until it is finally transferred to a computer. If you need an image in RAW format, you have to access the data via the menu item "Folder View".
By the way: I have testhalber times connected to the USB port of the data reader a USB card reader, which is otherwise used to a computer to read out all conceivable card formats. Thus I was able to access a Sony Memory Stick Duo from an older Sony camera, but only via the menu item "Folder View", then the DCIM folder, etc.
I assume that the other functions described work just as easily.
The particle is now an integral part of my photographic equipment!