I was in a fortunate position that I didn't have to rely on a student finance loan, so I can't advise you on that. I can give you the reasons I did my LLM: (1) I wanted to shift my focus to commercial law, and really specialize, (2) I wanted a renowned university on my CV, (3) I wanted the chance to network with big law firms. It ultimately bumped my CV up a bit. If you feel like that would be the case for you (and, again, you can afford it), then I would recommend it. If you feel like you went to a good uni for your undergrad and did well there, then definitely don't feel pressure to do one.