I'm not aware of any approved vaccine where the observation period was a mere four months and the control group was vaccinated thereafter. If there is another such vaccine, I would be hesitant to take that one as well.

There's no controlled experiment to suggest that mRNA vaccines provide a survival advantage to a healthy individual. The brief RCTs certainly don't support it. The increased cardiac risk, small as it may be, may well put the vaccine into negative benefit territory for some, but we'll probably never know for sure, because none of our data is robust enough to draw such conclusions.