My plan was once I reach official CEFR B1/2 in my target language. I won’t have to use LingQ anymore. I could just use language and consume content like a native and improve that way.
As for english (native), I have ielts C1 english. I think learning the exam format, strategy, tip and trick is very useful. There are courses on udemy that teaches that, how to deal with each section of exam efficiently to save time. Time is your enemy.
I mainly lost points in writing and speaking. I can get 8-9 points in listening/reading but for writing/speaking i get 7-8 points. I was actually too slow in writing to complete it.
For my case, C1 is good enough but If i want to get C2 i think i would get a tutor and work a lot on speaking, writing and maybe listening. A tutor who specilises in the exam can setup up a mock exam to figure out which of the 4 areas i need to improve. I think figuring out your weak area would help you focus and save time.
I’m not sure how lingQ would help, I think it would just slow me down. Since at C1 i can already consume anything without any aid (creating lingQ).
It would be interesting to know if someone has used lingQ as a main tool to get to C2 from C1.
For books and DRM just get Epubor
For audiobooks from audible you can use Audible Converter by Eupubor or Libation which is free.