hi! I took mine last friday, and I would say the official LNAT papers are the closest in difficulty. Leading up to my exam, I saved 1 official paper (did not read it at all) which helped a lot in simulating how I felt in the actual exam. I would say try out one of the official one's first to prep you for the types/language/format of questions. In my opinion, doing all the exams/questions available to you is very very helpful, even if they are not close to the actual difficulty of the exam or written similarly at all. Getting into the habit of being able to discern tone and inferred context is a skill that you need to practice over and over. As this rounds results come out mid feb, I'm unsure of how my scores fared in comparison to how I feel, but my advice is to really dedicate some time to the timed essay portion as well, it was much more stressful than I thought! (the clunky test keyboard did nothing to help, also there is no autocorrect so make sure you do a final read through to avoid awkward mistakes)
My school wifi blocked LNAT ninja, so I can't really say what they would be like compared to the actual one...Don't worry too much on how to "predict" your score, as my last days before the exams had a huge variety and I wasn't able to get any clear idea how I will do/did. Make sure to eat well/sleep well before the exams too and schedule the day after to literally sleep for 12 hours straight, because that was what I did.
Best of luck to you, you'll do great!