On one hand I do like the longer time course. I know some people do choose UK for this reason, saying that it offers more clinical time than US schools, which help them on the boards.
However, I think it should be explained that while you jump right into medical school from secondary school, US students must complete 4 years of undergraduate first. And while any major(s) may be chosen, every student intending to go on to medical school must take certain basic science classes. These classes amount to your 1st two years of pre-clinical years. Why US students enter into a 5 year program and not 4 is because some UK/Irish schools also start entering 2nd year students into clinical modules. Often times, pre-medical students choose a major which goes beyond what is necessary in med school, say...biology majors. They go into med school with a very deep knowledge base often including anatomy, immunology, basic biochemistry, which is then solidified and added to in med school, versus a UK 5-6 year program where everything is thrown at you at once. So I guess you can look at it as some pre-clinical material being covered prior to med school, and in this respect...I don't necessarily agree that the longer you're in school (i.e. 5-6 yr. program vs. 4 year programs) give you any better a foundation and are better. Longer programs might give you a bit more experience in a clinical setting. What I described above may also be a reason UK transfers to mid-school US programs don't happen.
And btw, not many UK med schools offer places to international students or have programs that are suitable for us. One of the major reasons I'm not applying UK.