When I heard that Zoku would be performing Koisuru at a concert (mind you this was a while ago), I immediately was slightly concerned. It seems like a fairly obvious choice; it's a proven crowdpleaser and is performed quite often. It's also one of the more simple v-u-den songs to sing; Koi no Nukegara is actually deceptively hard, Kurenai no Kisetsu is very underrated in being a difficult song to pull off, and the rest of them all have their issues to perform. The one easier song would probably be Kacchoiize! Japan. However, what both Koisuru AND Kacchoiize have in the original track (and in their original performances), is ENERGY. You have to be excited, pumped up, and be able to convey that to the crowd if you perform these songs. Now, this isn't a problem for the original v-u-den. Rika is a very dynamic performer (and I'm not just saying that) and obviously gives it her all; she has energy to spare and never looks bored while performing on stage. Yui and Erika followed Rika's lead and I think were great assets to v-u-den. Even though I'm a Rika fan, I always enjoyed watching the two of them perform, which says something about their ability to perform on stage.
However, Zoku's performance of Koisuru just falls flat for me in so many ways. Their dancing is slow and just looks bored, like they don't want to be there. That's how the rest of it is, really. Especially when they're not singing, they look bored and seem to just be going through the motions of the dance and not getting into it. And while most people often hate on the vocals of v-u-den, Zoku is much worse, in my opinion. This is one of the songs where the vocal quality honestly does NOT matter to me at all; the energy is king in any performance of this song. And here, it just falls flat.
This unit isn't bad together; I do like Only You, even though it's not my favorite thing or my favorite group off the album. They just are NOT in any way shape or form v-u-den. While many people accuse v-u-den of being the sexy unit, I'd actually argue that they are the mature H!P unit (and not having mature be a synonym for sexy). v-u-den was classy, especially in the songs/PVs of Koi no Nukegara, Kurenai no Kisetsu and Hitorijime (though the classy image is basically the driving image throughout their first five singles). Really, the two singles that were overwhelmingly sexy were Aisu Kuriimu to My Purin (which I think was supposed to be more humorous than actually sexy, but that might be just me) and Jajauma Paradise.
So, in my opinion, while the "sexy" is what sticks out to most people, v-u-den is to me the adult-type group. Berryz/C-ute are (or at least started as) the kids groups, Morning Musume has always had a younger age group, but v-u-den was formed when they were all in their late teens and went through until (at least Erika and Rika) were in their twenties. And while JunJun and Sayumi are technically older, I really don't think they have the adult-image that the others portrayed. JunJun, MAYBE. But anyone who acts as cutesy as Sayu, even though she's technically an adult, isn't cut out for the mature/classy group. Risako definitely has a sexy image, even though she's the youngest of the Berryz. But then, I think her age is what makes her not suited for the group. Now I've had it pointed out to me that Okada Yui was just a bit older than Risako when she joined, but really not by much. This is true, but Okappai debuted at that age. That's what the difference is. Risako has been around for much longer, since before she was ten. That really makes it hard to see her as adult-like/mature/etc.
This is a long rant that went nowhere, but yes. I'm now calling them Zoku without the v-u-den.