DD showed me this
www.revisionapp.co.uk/product/online-gcse-revision/?utm_source=facebook&utm_medium=cpc&utm_content=click&utm_campaign=RA+Clicks+1
£19.99 instead of £39.99 - I don't mind paying £19.99 if it's going to be useful to her but felt the need to ask 'the power of MN' first in case there's some hidden agenda where I am committed to monthly payments until she well through uni or there is some thread I haven't seen advising us to avoid like the plague 
All comments greatly appreciate in advance 