You will definitely have an advantage over students who only do strait economics if you want to work in finance. It is true that some employers hire people if they have a great personality (that maybe they had before going to uni, maybe they managed to develop it at uni during their spare time) and not for the subject they have studied, however this course will provide you with strong analytical and quantitative skills that will enable you to apply for all types of jobs (if you want to become a quantitative analyst for instance you can't have done classics), and it makes your CV very marketable.
Something that no one dares talking about, but which is very important is the ethnicity of the students in the course. It is a important to realize that there are over 70% of asians, espacially chinese in this course. So if you are from China for instance, you are likely to feel a lot at home, you will be very happy throughout these 3 years ! if you are international or have travelled a lot you are likely to adapt very quickly but if you are very british it is something to consider, and you might feel it is a difficult environment at first. If you look at the facts, there are distinct groups. To stereotype it, there is the eastern asian group and the non eastern asian group, which is quite small. From personal experience, as a non-eastern asian, you can become really good friends with an eastern asian individually, and you realize the myth of the cultural gap falls apart when you actually talk to them. However, it is rather unlikely to see a group mixing eastern asians and non eastern asians. I think that is due to the fact there are groups of people who speak cantonese, other mandarin and others english. That is why the social life of the department can be quite dead, so if you are a sociable person please do make sure that you are either in a sociable accomodation, either that your high school friends are near, or join several societies since the beginning of the year and fully commit to at least one. I strongly recommend this if you do not want to feel isolated. The department is probably the least sociable of UCL and before getting in I assumed it wouldn't affect me, the main objective was to get in because I knew it was worth it, so that I could concentrate on building a good career path. Well of course, it is something you shouldn't loose sight of, and it varies for everyone, but I did feel quite lonely during my first year.. And it did affect my emotional health, which directly was directly linked to my academic performance.