Broadly, the prospects for someone with a B Economics degree are somewhat similar to that of Finance/Commerce/Management/Business graduates. You'll (almost certainly) not be denied any position that anyone with those sorts of degrees can get on the basis of your Economics degree.

If you took a job like that it would be what I'd describe as a "normal" or average job - since so many different types of people can get many of those types of jobs (sometimes even without a degree, let alone one in Economics). But it is a big pool - it could be a decent job like a graduate management position, a trader, an investment analyst, a banker, or it could be less impressive, like a job in operations, or administration, where no important decision making is involved.

What would set you apart (though not necessarily be desirable, unless you were heavily interested in Economics post-degree) might be an Economist position in a bank or research or investment firm, although that might require further qualifications. Let's not even discuss academia since technically that path is open to anyone who goes to university.

Then there are those non-traditional paths people take after their degree, to become Accountants, Auditors, or Actuaries.

I think there's not much you can use of Economics in most jobs. The important bits have already been exported to Accounting, Finance, Management and Business Administration etc. You'll be hired for your analytical ability if that's what the job requires, otherwise you'll end up no different than the vast majority of Commerce/Management/Business graduates.

To go far in academia you would need a PhD. But you don't actually need to have a PhD to teach at undergraduate level... suppose you don't know how far you'll study at this point. It doesn't matter. Maybe during your BEcon you discover you like to research (and teach) Economics, but in an academic setting and not for an investment firm or bank, or you're not even sure, but you aren't ready to work... then you might want to pursue an MEcon and after that, if you haven't decided you want to go outside of academia, you can teach while pursuing a doctorate. Anything can happen. There are opportunities in Business schools and Economics schools, there is also work outside academia, but everything is relatively competitive.

They aren't that different in terms of prospects, but if you wanted to study graduate Economics (which you don't know now, of course), then the pure Econ degree would be more helpful.

Otherwise you could get the same jobs studying either degree.

Economics at the higher level is hard. Particularly the Mathemathical and Statistical aspects. Not as hard as some intense subjects (like Mathematical Physics, Theoretical Physics, Pure Mathematics etc), but certainly harder than softer subjects (in a different way) like Business, Management, Marketing, Arts if you're good at essays.

I wonder if you've ever studied Economics.

It's not comparable to a subject like Maths... as in the majority of early-year/introductory Maths courses at university will require a degree of background, while it is the complete opposite for the vast majority of early-year/introductory (undergraduate) Economics classes (the same for Finance, Accounting, Business). There won't normally be assumed knowledge. And this applies to core subjects.

In other words, Economics isn't on average very hard for students without a background in it. Some people with graduate degrees in Economics didn't even do undergrad Econ degrees (but obviously a diploma or relevant qualifications/experience is required to do such degrees at any reputable institution).