I realize this community is probably dead but I figured it wouldn't hurt to shout into the void if it is.
I enjoyed making my own yogurt in the past but got annoyed with babysitting my makeshift incubator consisting of a cooler and an electric blanket and stopped. Recently I took up yogurt making again but this time with mesophilic cultures. Being able to just leave batch of yogurt in a warm spot in the kitchen until it is set is just so handy. I'm also looking forward to trying some different cultures. I've got filmjölk and a viili cultures in the freezer for when I want to change things from the kefir simulate culture I've currently got active.
I bought them from here since I used them back in the day when I was doing the thermophilic culture thing and so I went back to them for the mesophilic cultures. It is part of why I'm doing a kefir simulate culture rather than grains as they don't offer grains. If you look around online you'll see other businesses offering mesophilic cultures as well.
With something like viili there will be a noticeable texture difference from what I've seen of people making it. Most places selling cultures will have some notes about what sets it apart (e.g. I see filmjolk called distinctively buttery on multiple sites). I don't know how subtle those differences actually are until I get around to trying them and I imagine someone selling yogurt cultures for a living is probably more tuned into such things. I imagine plenty of people would just go, "It tastes like yogurt to me."
Edit: I can say the kefir-like I'm making lately has more of a fresh milk taste compared to thermophilic yogurt I'm familiar with. Though that could easily be differences of preparation showing themselves rather than anything to do with the culture specifically.
Just wanted to give you a bit of an update since I've finally got around to making some filmjolk. I'm still trying to nail down the fermentation time but I'd say that yes, I do notice a difference between it and the kefir I was making. It does have have a buttery note I mentioned, which I like, and I'd say it is a touch less sour. At some point I'll get around to trying a viili culture and get to play with it's interesting texture and note any flavor differences.