This can earn the average if one is tolerant, and if one is willing to take the time to compare the explanations given to the reality on the machine, and official documentation.
On this condition, it is a play that will be profitable because some subjects (this is unfortunately not the case for all) are quite clearly presented. However, patience may be sorely tested to the errors whose work is enamelled, including answers to end of chapter tests.
However, it would be very risky to spend certification with this work only source of preparation.