I was in this exact place last year and I wish someone could have answered this.
I’m not too sure how any of the finance works but you get paid for your pre-reg training year. However, if you do the 5 year course, you’d have to pay 9k extra for your training year as it’s part of the degree. So in my opinion, you’d be better off doing the training year separately after you graduate from the 4 year course. The only benefit that doing the integrated pre-reg course holds is that it allows international students to complete the training as part of their degree for Visa-related reasons.
I ended up applying to both the 4 year course and 5 year course thinking that it could help my chances- it didn’t! I just got an offer for UCL MPharm thankfully but my second option (integrated pre-reg) got automatically disqualified, so don’t apply to both if you were thinking to.