Well, it is impossible to learn by heart any materia medica.You have to take help of repertory and for confirmation it is necessary to consult a reliable materia medica.This is the best way.
Sometimes a remedy is mentioned in the repertory and is missing in the materia medica.
'Knowledge of repertory' means the knowledge about its plan, construction, philosophy, availability of rubrics etc. It is not a memorisation of its contents. It is possible for any body to aquaire such a knowledge if he tries to. If a doctor is depending only on a repertory without its basic knowledge chances of failure are more.
Knowledge of Materia Medica is not like that. Knowing of the plan, construction, or such things are of less importance. One should memorise the symptoms - at least the essentials. That is a task impossible for an average man. Hahnemann himself was not in a position to do that. We know that he kept the index of symptoms for reference.
So, in my opinion, someone who has a good knowledge of Repertory and its application and less dependent on Materia Medica is better equipped to generate an accurate prescription - in less time and with maximum confidence.
I believe that the final stop must always be the Materia Medica for a simple reason: homoeopathy is a medicine of the whole. The repertory, as important as it is, divides the whole into myriad parts. If one skips the final step, of reminding oneself of the remedies in the entire sphere of their activities, in the wholeness of their individual healing sparks, then one is too likely to target with his or her treatment upon the hundred details--the symptoms--and not on the whole being--the patient.