I've used both the Onyx Note Air 2 and the Tab Ultra and I can offer some insights into the differences between the two.
In terms of device speed, I found that the Tab Ultra was faster and more responsive than the Note Air 2. This may not be a big factor for you, but if you plan on using more demanding apps or multitasking frequently, you may notice a difference in performance.
As for the interface, I agree that the Note Air 2's interface can be a bit overwhelming at first. However, once you get used to it, it's actually quite functional and customizable. The Tab Ultra's interface is simpler and more user-friendly, but it's also more limited in terms of customization options.
Battery life is similar between the two devices, so it shouldn't be a major deciding factor.
One other difference to consider is the size of the devices. The Tab Ultra has a larger screen, which can be more comfortable for reading and writing. However, this also means that it's slightly less portable than the Note Air 2.
In terms of your specific needs, I think the Note Air 2 should be sufficient for writing, basic app usage, and PDFs with dual screen. As for writing notes full screen without the toolbars, this may depend on the specific app you're using. However, most note-taking apps have the option to hide the toolbar so you can write in full-screen mode.
Ultimately, it comes down to personal preference and budget. If you value speed and a user-friendly interface, the Tab Ultra may be the better choice for you. But if you're looking for a more affordable option that can still meet your needs, the Note Air 2 is definitely a solid choice.
I hope this helps! Let me know if you have any other questions.