The interview process was quite rigorous, but that's a good thing. Company wants to make sure you are truly a perfect match for the position and this also gives you an opportunity to get a better idea of the role and company's culture.
Another positive thing is, that the interview process is very well organized. I had to pass several rounds of interview, but the HR people tell you at what time EXACTLY they will try to contact you, so you can better organize your day and you don't miss a phone call while on tube etc.
Also, they don't ask stupid questions like "what kind of tree or animal you would like to be". Instead, they really try to understand as much as possible what type of person you are by simply asking questions about your professional background and interests. I liked this "down to earth" and "humane, honest, unpretentious" atittude.
In short, it was actually quite a pleasant experience. Was I nervous during those interviews? Of course I was! But he best thing (at least for me) - I work for Dataminr now and the first impressions are only great.
I guess everybody on Glassdoors mentions it, but free lunch is really a cool thing! It helps you to save money and the company is quite generous in their meal allowance. Last, but not the least, no matter what department you will be working in, the people at Dataminr are super-friendly, intelligent and helpful. Company also offers a ton of other benefits like medical insurance for you and your family, free dental care (very expensive in Britain comparing to... let's say...Germany), stock option buying scheme and many other perks.
Finally - the salary is quite competitive too and you have a feeling like they want to invest in you and they are hoping you will stay with the company for many years. It's a start-up which is rapidly growing, therefore a perfect place to growth in your career.