I tried Retopoflow few times, in different stages of development.
And two thing never change about it: slowness and bugs. I gave last chance, because someone told me it is different and nice now… But… One big thing changed: now it have totally separate interface and standart operators do not work with it. So I loose all power of blender in exchange to few weak tools.
It looks designed not by blender users, who prefer hotkeys, speed, universal and flexible tools.