well, i used seneca for my gcse science and i loved it, i didn't know they have btec applied science on there, so i will definitely be check it out... I went and checked it out, it look good so far.
And I would say its free, and its extra revision/practice so it wouldn't hurt to use, to revise i would use seneca, the specification, flash cards and practice questions, also always go through what you don't understand in class at home, and never EVER be afraid to ask the teacher a question.