Don't know anything about Singapore Maths, but had experience of similar system.
I think the advantage of it is that it will let most of children have a solid math foundation. But I don't think it will stimulate the bright, able children much. I guess bright and most able children would normally take extra stuff outside classroom in Singapore.
Like when I was little, there are no after school tution exist in my country, teacher would put challenge questions on the board every week. you would get a reward for being the first one to solve it. There were exciting compitition between a group of boys and a group of girls in my class I remember.And now, there are after school math class teaching Olympiad math for the most able children. I think Olympiad math is quite different from the normal math, it is more a kind of intellegence challenge.
I hope, UK won't just simply adapt Singapore math, but use the approach to help most children gain solid foundation, still keep the differentiation for the bright students.
Just mention, I have to say I am surprised to see some of my colleagues (who have been to University, of course learnt non science ,engineering subject) can't work out average, percentage.