There is not a single disadvantage infact I have a list
1- problem in gear shifting, becomes very harde even after few kms of eservicing
2- vibration level is very high even at a speed of 50 kmph the vibration frequency is so high that u cant eve think of a long ride
3- suppose u dont use your bike for lets say for a week , then it just dont use your bike for lets say for a week, then it just dont started untill and unless you call a mechanic