Hey Emanuelle,
thanks for asking :D I wanted to post something but I'm actually not there. After I posted a Jam with the OT, I stepped back and made the OT my mixer and arranger who controls the sequences of Digitakt and Digitone for now. I'm using the OT in my latest live sessions too, sequencing the Peak with it. You can find them on my YouTube channel, especially the session from August 25 shows the OT in action. But I don't use it for sound mangling or processing for now, it's something that will come later.
To make that clear, because I read this often: the Octatrack is NOT an upgraded Digitakt nor is it an extened version of it. It's a completely different system with a different approach! Digitakt also doesn't feel like the little brother of the OT, which means that I'm not passing from the Digitakt to the OT. Right now, I have the impression that it's a good but complicated counterpart and a good central machine for my setup.
Is it worth it? Well. I'm currently working on some 1-hour sets and the arranger alone takes away a lot of stress, especially with a setup that uses more than the Digitakt and Digitone. Just because you can control the other gear with the arranger too. That is really helpful. Regarding sound design, I'm not there to tell you if its worth it or not.
The learning curve is high because there are many unlogical button combinations you need to learn, and the data structure is far more complex than the Digitakt. For instance, parameters. Digitakt stores these TOGETHER with a pattern. That means, if you change the pattern, you change the parameter set as well. Octatrack stores these separated from the pattern itself, that means when you change the pattern, the paramater set stays the same until you switch to another paramater set ("Parts"). That alone raises the complexity of a project massively, but gives you more freedom. There are other elements like scenes, sample information and sets that you don't know from the Digitakt, and all these you need to learn first.
For me, I am discovering the OT slowly now. With each new jam or set, i am exploring some of the OT features step by step. That's the reason why you have not seen a pure OT Jam until now :D I just don't have done it.
I hope that helps a little :D Cheers!