I guess it all depends how you use the Jetbook and the computer operating system you use.
I use Linux, and don't connect the JB to the computer at all. I have an 8G SD card which I put my books on. I convert all to pdf as I find the performance superior. My books then usually go through these stages: <some format> to epub (using Calibre) to pdf (using one of the epub2pdf converters - I favour Jelby's off this site).
Jelby's epub2pdf produces very smart books formatted nicely. It can be found here:
https://www.mobileread.com/forums/showthread.php?t=89689
but is for Linux only users. There is another here:
http://epub2pdf.com/
Perhaps there are other Linux users who would find these things useful.
--Tony