The TOPIK II exam encompasses of level 3-6 which is a wide range of ability levels. As such the difficulty level of questions also varies widely with a pre-defined proportion of questions set for each of the difficulty levels within the same paper.
Should I take TOPIK II as an intermediate learner?
The Listening and Reading papers of TOPIK II starts off with questions that are probably very manageable for intermediate learners. However as one moves along the paper the questions get harder very quickly. There are simply too many questions which are beyond an intermediate learner and have to be skipped altogether or attempted by wild guessing.
For the Writing paper 50% of the score is allocated to a long essay question. There is a risk that at this stage an intermediate learner does not have an extensive enough vocabulary and fails to grasp the meaning of the key words in the question, hence losing a whole 50 points out of the 300 total.
If one takes the TOPIK II exam intending to attain level 3 or 4, one will be aiming at a score of 120 and 150 out of a total or 300 respectively. That translates into 40% and 50%. There is not an unattainable goal. However having to deal with questions that one is fully aware are beyond his level can be frustrating and hence not productive. Some kind of strategy is also needed on which questions to skip to save time. Instead of spend your time and energy on the exam, why not focus on advancing your Korean to attempt level 5 or 6?
Therefore unless you are trying to apply to a course or job which requires a level 3 / 4 qualification (which I doubt there are any), I personally do not find it very meaningful to take TOPIK II with a target of level 3 or 4 only.
Having said that, since the exam fee is not too high you can just take it for the sake of completing a milestone in your Korean learning journey or getting yourself familiar with the TOPIK II exam format. You can find practical killer strategies to TOPIK II here.
One thing to note though is that since the 64th TOPIK is the last time the past paper is officially published by TOPIK, past papers which are extremely valuable in the exam preparation becomes a scarce resource. That means that the 35th, 36th, 37th, 41st, 47th, 52nd, 60th and 64th papers (8 in total) are all there is for you to prepare for any TOPIK II exam. The time allocation strategy is very different when you are targeting level 3 vs level 6 so be careful not to use up all of the past papers to practice so you are left with no official materials when you try to attempt level 6 later. There are always mock exams in TOPIK preparation reference books that you can buy but the question setting may not be up to the quality or consistency level of official past papers.