Pros
As you can read from pervious reviews, the first pro about HackerRank is that it is the best product in the space (and, from direct experience with prospects/customers, its not even really that close ). But, for me, the best part about HackerRank is the people. The CEO has a strong and clear vision about where the company is going and is always available to hop on a customer call with you and meet with you directly for any reason. The same can be said about leadership across all verticals, everyone is approachable and willing to help and do whatever is needed to move the company forward and ensure the customers are happy. It's a cool experience to really enjoy everyone you work with and it's led to a open, collaborative environment on the floor. Work/Life balance is fantastic with reasonable expectations set out from day 1, and, as other reviews have mentioned, the perks are pretty generous.
Cons
It's a start up and has the associated traits - it's not perfect. As they continue to disrupt the technical hiring market, inevitably there is going to be change and growing pains. However, this contributes to the excitement of working for the company, as they grow you have to opportunity to make a tangible impact and see it in action.