The long term safety data on dutasteride is actually reasonably reassuring. It has been approved for benign prostatic hyperplasia since 2001 and has been used continuously in that population for over two decades. The cardiovascular signal that appeared in one early trial has not been consistently replicated in subsequent larger studies.
The main side effects are the same as finasteride but potentially more pronounced given the stronger DHT suppression. Sexual side effects, reduced libido, ejaculatory changes. These affect a minority of users and for most resolve when the drug is stopped.
The longer half-life of dutasteride is worth knowing about. It stays in the system for weeks after stopping rather than days, so if sides appear they take longer to clear than with finasteride.
There is no strong evidence of lasting hormonal disruption from long term use in otherwise healthy men. The prostate population has given us a long follow up window and the picture is broadly safe.
That said, it is a more aggressive intervention than finasteride and the decision to use it long term is worth discussing with a doctor who knows your full health picture.