Aviationinsider レビュー 

Great value for money and customer service.

Bought a KSA 100 Preparation Course for OVER 20euros just to practise mental maths all you get is arithmetic operations that you can practise on your own (was expecting stuff like TOD, dme arcs etc.. but none to be seen there) and worst there seems to be mistakes there for example whats 9.20% of 150>? they say its 9.30 lol clearly its 13.8 not that you will need these kind of calculations with decimal percentages anyways.

As of non mental math part everything is pretty useless you can find all of that for free on net if you really need that, for me hardest part is mental math so I sadly bought this..

Just skip this one and go for some youtube videos and practise multiplication, divisions, percentages on your own...