Meds- Apical Hypertrophic Cardiomyopathy

Hi My friend is 29 years old and as part of annual heart checkup consulted with a cardiologist, who suggested ECG, Echocardiogram, CBC, Lipid-profile, Creatinine tests (reports & prescriptions attached). The reports suggest a mild Apical Hypertrophic Cardiomyopathy. The doctor has recommended T.Prolomet XL 12.5mg daily for next 6months to lower the heart rate. He was diagnosed with HCM several years back - took Inderal-10 for few years (around 15years back) but stopped the medication on recommendation of reputed cardiologists (consulted 6 and 3years back). Currently he is not on any meds. So he wanted to check if he should be starting on T.Promolet. Also, are there any side effects and is it something that once he starts taking needs to continue for life. Please suggest on what is the right decision. Regards.