A lot has been mentioned in the previous answers about the online CAT courses. I would be focusing on a different offering by 2IIM - their online Interview preparation videos.
2IIM is famously known for providing free trials to their courses. They are also quick to respond to your enquires and mails. Overall they provide a very personal and refreshingly new experience to one's CAT preparation journey. It will definitely be worth the effort to check out their website. As the saying goes - 'Pehle sab try karo. Fir sahi chunno'
In one word : Amazing.
I think it was in the 3rd year of my Engineering when I came across an online advertisement of 2IIM. I visited just out of curiosity for the name 2IIM. It sounded so interesting. But I was not really preparing for CAT then. Then, in 2018, when I was finally jumping in to take up CAT 2018, I had hardly 100 solid days left for Preparation. I had to start from the scratch. Literally. Then I remembered about 2IIM. And watched Rajesh Balasubramanian Sir's recorded video sessions for LRDI Section. They were Fantabulous.
I first heard about 2IIM through their YouTube videos in the year 2018, just after writing CAT 2018.
I will get into the technical aspects of my review, but before that, let me also mention that the 2IIM team has a wonderful way of approaching the exam and providing timely advice whenever asked for some. Time and time again I asked for advice from Bharathwaj sir, and I was reassured and encouraged through my CAT prep in its entirety. Rajesh sir also casually reminded us to not give into percentile calculators, PagalGuy, and rumours.