When you get right down to it, Franken Fran is nothing more then a B-Horror story that relies more on guts and gore then on actual story. At the most, it can be called a guilty pleasure, at the least it can be plainly seen as a series that is trying way too hard to try to be scary. Sure the talk of all the gore and etc would draw and fascinate people to those who just hear it, but what they end up getting is a Manga that replaces character depth, sensible writing and even scariness with just plain gore.
The fact is, people say all the graphic imagery is supposed to be scary, but when you get down to it variations of the same could be seen in other places and even better. This series runs on the concept solely on doing two page spreads of horror which after awhile, turn into the Manga version of a Jump Scare. Which like all others of its kind, loses it's scare factor over time. People say the character of Fran can be seen as childish or just not understanding of what she does. Yet after horror upon horror she that she performs on other people: It hits you eventually that she is neither sympathetic, nor a likable character in anyway.
In the end if you like it, go right ahead and read it. But as it is story-wise it becomes undefendable, and scary-wise it becomes boring.