From the official Ectaco page
http://www.ectaco.com/jetbook-mini-black/ : Support for LIT, MOBI, EPUB, HTML, PRC, RTF, PDB, PDF via Calibre conversion to TXT and FB2.
I imagine the limited format support is partially because the processor must be less powerful than JBL. Surely, it is not because someone is afraid of cannibalizing Jetbook and JBL sales...
Still, Calibre conversion of PDF to TXT ? That is not going to look pretty, none of the pdf to txt conversions, I have done, have come out well on my Libre. Then again, this is regular txt we are talking about.
On the other hand, I am extremely happy how PDF reflow is handled on my Libre.