Android is in this regard apparently quite bitchy, of 2 existing multicard readers not functioned reliably. This reader works fine, 8 different CF card (Sandisk, Hama, Calumet, Sony) were accepted.
The most reliable way it seems to work, if only the card into the reader and this is then plugged into the USB port. That seems a bit like voodoo, but brings reproducible results.
The here sometimes criticized mechanical instability of the card guide is comprehensible way. Responsible for this is the very short length of the guide rails which receive the cards before they are placed on the contacts. This requires, in contrast to the card slot in the camera and to readers with greater overall depth, a lot of sensitivity when plugging.
This is unacceptable from my perspective - especially if there are otherwise no electrically functioning for Android Reader.
