JefeCheck

JefeCheck is an awesome flipbokk app that is now available for free. Check it out here

This script is a very basic implementation that makes JefeCheck appear in Nuke's default flipbook panel. Not all options offered in the panel are supported.
Drop the downloaded file into your plugin path and the following lines into your menu.py:

os.environ['JC_PATH'] = '/Applications/JefeCheck.app/Contents/MacOS/JefeCheck'
import JefeCheck
nukescripts.setFlipbookDefaultOption("flipbook", "JefeCheck")

The first line will tell the script where to find JefeCheck, so change it according to your system.
The secont line will import and regsiter the JefeCheck flipbook, and the third will make JefeCheck the default option in the flipbook panel (instead of FrameCycler)

This has only been tested on OSX.