Pros
Not many other companies provide the ability to work at this scale. Depending on what you end up working on, your work has the potential to affect millions of people and drive serious revenue. It's a recognizable brand that will look good on your resume. Many people that have had a successful career at Klarna have gone on to leadership positions in other companies afterwards, so building a network while you are here can lead to good opportunities in the future.
Cons
Upper management actively despise their employees and do their best to force attrition and burnout by removing perks, enforcing unpopular policies and applying more and more pressure. There is absolutely no investment into the employees, such as via training, mentoring, or even providing basic resources needed for the job. The result is a cutthroat environment where people compete, rather than collaborate, in fear of losing their jobs. It was not always like this, but it has gotten worse and worse over the years. Because of the immense pressure from above, middle management is rife with politics and getting anything done requires navigating a sea of toxicity. You would do best to try to stay out of it as much as possible. This is not necessarily a reflection of the individuals, but of the environment they find themselves in and the pressure that is put on them. Where previously teams had a lot of autonomy in driving the direction of the product they work on, there is now much more micromanagement and the only way to not find yourself on your way out is to be a yes-man. There is an extreme focus on standardization in tech, which has real benefits, but a drawback is that the average engineer will rarely get to do any actual engineering. If you are happy building products by integrating components, then you will likely enjoy this, but if you want to gain a deeper understanding of how technology works, you may find this frustrating.