I registered on Gmatclub 4 months ago and I'm still preparing here. Actually, it's even not necessary to use any other source of knowledge. Here I found a lot of difficult problems with comprehensive solutions, good mates, who can explain difficulties. My mates said that tasks from this forum are extremely similar to real GMAT and I really like the fact that I can practise on such different and complicated problems. Also, I would like to mention that Verbal tasks are also well developed and provide good explanations for each question.
I haven't passed my exam yet, but now I feel much confidence after this 6-month studying plan. Good Luck to everyone!