I tried the app, as it's available on App Store, it didn't surprise me how this "vertical anime" weren't given all that care and production quality. For starters, the point system was very frustrating cause you only get 2 points per ad you watch so to rent a 40-point video you had to watch tons of them, at some point if I recall correctly it would stop either showing you ads or giving you points for the day. I bought a total of 3275 points to see two series that were fully subbed in English, I'll get to that later, for around $27 dollars, I bought them because there's an option to do that, 40 points for renting a single episode, 85 to have it "permanently" in your account. They were almost like slide shows, the kind of animation seen in Yami Shibai. Sadly I made the mistake of not making an account, still, it allowed me to purchase points, so it's my own fault as sooner or later (and now because of the end in service) it could boot me off. The service wasn't just anime, it had some "Voice" things which I guess were the equivalent of drama CDs or something like that. It was a small app to begin with, at least in my region, so I have to guess the article saying it had Production I.G. series such as Attack on Titan was exclusively referring to the Japanese version of the app.
Now on with the shows, I coincidentally picked two anime whose manga come from the same magazine, "Manga Goraku", which were Monkey Peak and Gift±, the former covers 21 chapters (3 volumes) and boy does it show! It can't catch a break and doesn't let any of the horror atmosphere work because of it's pace (2-min episodes), the latter adapted 5 chapters so it worked a little better, a little because this two were divided into 20 episodes meaning that you really had to rent all episodes to have something substantial cause they were nothing by themselves. I read all available scanlated chapters at the time (2021) of both, and while they're both kind of edgy they were a bit more enjoyable in manga form, especially Monkey Peak. Btw Gift± is a gory series about organ harvesting but the anime is censored in its free episodes and on the ones you can purchase, why censor your anime in your own streaming service? Beats me. Vertical anime was a weird novelty (sort of like what Quibi was for the West) that idk if it became popular in Japan. Hopefully, they upload the series to Youtube or another streaming service, otherwise all that vertical anime catalog will be lost.