It's hard to say.
It very much depends on what you stand to learn from the experience and how the rest of your portfolio of experience would look like. A 1st will help you stand out from the sea of 2:1s, and if you have good evidence of research skills (RA post), published your undergrad dissertation, you would have demonstrated that skill. However, people do get further skills on MScs + contacts and can reflect on these at interview. It certainly won't hurt.