Praise be to Allah.
The “five fortresses” method for memorizing the Qur’an is a method based on a plan for preparing the pages that one wants to memorize, a method for memorizing and a method for reviewing what one has previously memorized.
It is a method that includes reading from the Mushaf, listening to a skilled narrator, repeating what one wants to memorize, then reviewing what one has memorized without looking at the Mushaf.
Based on that, it does not seem that there is anything objectionable about this method. Rather it is a good method that connects the Muslim to the Qur’an on a daily basis, and gets him used to reciting the Qur’an and not forget it. It is well known that educational means and methods of reviewing and memorizing, and the like, are only means of acquiring knowledge and memorizing and reviewing the Holy Qur’an.
The ruling on these means is that they are permissible, so long as Islam has not forbidden them.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
If a method is not forbidden and it is effective, then there is nothing wrong with it. Means are not the same as objectives, and it is not essential that Islam should state for every means or method that it is permissible or otherwise, because means and methods are innumerable and unlimited, so everything that is a means of achieving good is good. End quote from Liqa’ al-Baab (15/30).
Moreover, when determining whether a particular method is better and choosing it over others, we should look at experience and what is best suited to each individual. What is suitable and beneficial to one person is not always suitable and beneficial for another; rather it may be suitable for someone else, or some other method may be more beneficial for him. So each person should look at what is most suitable for him and will help him. The Prophet (blessings and peace of Allah be upon him) said: “Strive to do that which will benefit you and seek the help of Allah, and do not feel helpless.”
And Allah knows best.