It's not generally a vocational degree. It's likely to be about as good as Accountancy for becoming an accountant (though an Accountancy degree would give you exemptions from a lot of the professional exams and potentially shows some interest in the job) and better for everything else. I know three graduate trainees at PWC. Two studied History and the other Maths. Economics is better for becoming an economist, but for most things they're going to be pretty similar. Maths graduates that I know generally ended up in banking or programming.
Most jobs don't require a specific degree, so the big thing for employability is getting a 2.1.
Maths, like all subjects, is different at university, so there's no guarantee that you will like it. But it's not a bad degree for employability, so you might as well choose on enjoyability.