Nobody knows the long term effects of them because they've never made a vaccine in this manner before. In theory is ok, but another theory says they'll alter your DNA!
It's pretty well understood what this can do. There is no real chance of some horrible long term effects. Any such one in a million case will matter far less than Covid.
I know how it is made. It is a great new way to easily produce vaccines. It has no way to cause the problems some people imagine. Science is not magic. The outcome and a not random.