Generally speaking a lot of people here don't like Duokan ) It's big, it's often flawed and their developers often steal code from this forum without acknowledgements. That's why developers are annoyed.
Duokan has no English support or forum(known to me) but you can find a lot of related info using Google Translate and
their current thread on MIUI.
Duokan is an alternative operating system.
Duokan does not delete the typical Kindle OS, so you can dual-boot back and forth as necessary.
But there are drawbacks:
Encrypted DRM AZW files from Amazon's Kindle store cannot be read.
Wi-Fi Only. Duokan cannot use 3G of any kind, and never will support it.
You can't use Goodreads service integration and Amazon Dictionaries or any other Amazon related stuff (cloud, search etc.). *(Which you can in standard OS)
On other hand you can install and use KUAL and KOreader without a need to change OS(reboot) every time and KOreader has a lot of great features, if you'll need more interface integration you can find more stuff and hacks on this forum.