I think FF fans would like this story, but as for WDTFS fans, I'm not sure. The story hasn't had any plot twist so far, everything is predictable. :)
I think it's more like WDTFS than FF. The art, the age/experience gap, the ex-girlfriend who looks like she really wants to spoil their lovey dovey fun. Obviously WDTFS is more explicit, but you can make a lot of easy comparisons between Erae and Sungji.
Yeah, Erae character did remind me a lot of Sungji, although I did find her actions, behaviors, how she fell in love, and how she came to her conclusion that she was in love with Yoon more reasonable than Sungji's. But YoAhn character is not similar to Seju's at all. She has been presented as a psycho ex since the beginning of the story. I doubt there's any reader who could be her fan, or could ship her with Yoon. As for Yoon, she's smart, she isn't a kind of person who can be manipulated by anyone, unlike Sumin. Also, since she has never been stuck in a tragic relationship with YoAhn after the breakup, she sure can easily move on with Erae. No wound needed to be healed, no other potential pairing, no angst, ...., therefore, wdtfs fans who I think they seem to prefer plot/drama would think of this manhwa as nothing but a typical kdrama.