Hey,
I can't answer your question regarding if UpLearn is useful for physics or maths because I took neither at A-level BUT I did take economics and bought UpLearn around 6 weeks before my end of year 12 exams. I went from a U to a B in the space of 6 weeks just from using UpLearn and 2 days ago found out that I got an A in economics all thanks to UpLearn.
I would really recommend it (speaking as an economics student).