The Wallflower manga is...less good than the anime. Part of it is just a translation issue with the earlier scans (Evil Flowers takes over at about volume 25 and they do a great job!), but really, everything about this series works better in the show.
Art-wise they’re both weird, but least the anime has color which helps a lot because other than hair style and color, everyone looks pretty much exactly same. Especially our four main bishounen, like - in the manga, every time Kyohei gets his hair wet he looks exactly like Ranmaru, and it will sometimes take a few panels to realize who is who.
The anime doesn't have much of a plot, but it's harder to tell in a shorter format and arguably the last episode shows some progress (and everyone does at least seem to grow character-wise). The manga, however, has zero plot. In theory, the goal is making Sunako into a lady, but they never make any progress on that front and the stakes of not doing so (triple rent) are pointless when they aren't followed up on. (Obaa-san discovers that Sunako's made no progress and says she's going to collect from all of them/just Kyohei at least three or four times, and yet...nothing changes.) Also, the stories 100% start repeating (which makes sense, because no one ages in this manga; we go through at least three valentines days/christmases/halloweens, and while they reference previous years, no one learns anything or moves up a year in school or talks about growing up or colleges or jobs or anything). The stories not just similar, though, but literally the exact same scenario, like when Sunako tells Kyohei she hates living with him, Kyohei leaves and wanders Japan meeting up with strange people, and Sunako makes a big show and apologizes and he forgives her and comes back - this exact thing happens twice, with no mention of the previous time!
Also, character-wise, they're all basically the exact same people they were at the beginning (except Sunako, who doesn't change her personality but does become willing to tolerate other people). Romantically, everyone does make (some) progress in the manga: Noi and Takanaga kiss a couple times and are officially in a relationship, instead of everyone just assuming they are; Ranmaru is nice to Tamao and accepts that she is special to him -- though mostly due to manipulating from other people and while still playing around with women; there was a moment where Sunako and Kyohei seemed like they were going to realize their feelings for each other, but instead they just decided they were friends. Basically, though, everyone makes that amount of progress in the anime, and I didn't have to read 120 chapters of filler and backtracking for it to happen. Also, they bring in the other female characters a lot more in the show, which is great because yay, female characters, but also helps make the relationship growth between everyone seem more interesting and realistic; Noi and Sunako become friends almost immediately in the anime and then Noi shows up almost every episode, and while Tamao is introduced later, she then appears in almost every subsequent episode as well. The anime even goes so far as to include girls in places that they weren't in the manga in order to have a more balanced cast, which is pretty cool.
All the characters seem like they are more likable in the anime as well, and also, you know, they have actual growth there (even though we spend so much less time with them). For example, in the show, while Takanaga is nervous and hesitant about his relationship with Noi because he was sheltered growing up (and also because any time he does anything romantic with her his friends make fun of him), he definitely genuinely likes her a lot; in the manga he’s sometimes portrayed this way, but other times he's kind of just a dick. Also at one point,
the other boys and Sunako’s aunt lock Kyohei and Sunako in a room and tell him to rape her to make her a lady. This manga has portrayed women attacking the men and ripping their clothes off a lot with the men being rescued just in time, but it’s almost always to comedic effect - which is not really okay either, but it’s more okay than this scenario, which is 100% serious, just barely doesn’t happen, and then is never mentioned again. But also from a character point of view, it’s really weird of all of them to do this because they have all been shown to be friends by this point and to care about each other – and Sunako’s aunt not only supposedly loves her like a daughter, she has also proven that she won’t raise the rent (even if she threatens to) if Sunako doesn’t become a lady; so, even if they were being terrible and just doing it for the money, it makes no sense.
All in all, while parts of it were fun and made me laugh, I can’t really recommend this manga to anyone. It’s long and pointless and nobody grows up, and the jokes from chapter 1 just aren’t very funny by chapter 105. Watch the anime though! I’ve watched the anime a bunch of times, and it’s everything this manga could/should be.