like heruru meruru said, most vocal synth designs and re-designs don't get wide-spread hate.
Most of the hate for character's designs are personal prefrences among people who actually vocalise them or vocal minorities. I know a lot of Kaito fans used to not like his V3 design, or just prefer his V1 design. I saw reasons as silly as "I can't make public nudity jokes with him wearing only a scarf with this design anymore" from 2013, to "It looks like that jacket has no room for him to breathe in and the materials look uncomfortable to have on your body" a friend of mine expressed. And Synth V Teto's outfit has a military motif that some people find uncomfortable, but some find cool or don't let that stop them from making their own teto designs.
And most of the one's people do nearly unanomously dislike often don't really get popular enough to cause a big stink. I had another friend recently show me +s ome other friends the Genbu + VirVox rebrand designs after some internal conflict with the company and the artist I didn't really look into, and they're... pretty rough... most of the chat agreed as well. Though that friend was the only person I knew that even knew about it and showed to the rest of us.
Finally, most of the universal dislike for certain characters designs i can recall have the artstyle play a huge factor as well. Sonika's inital V2 design used a 3d model that made her look like a character from a xbox game with no real art direction other then "WE HAVE TO HAVE REALISIM". and the v5 included vocals have the same jank 3d model problem.
