They're ideal for defence, and can't really be used for attack due to their small range, inability to land on aircraft carriers, and high research and production times. Also, they're expensive compared to interceptors, require secret labs as well as airstrips, and unlock very late in the game compared to interceptors.
I would say they're pretty balanced for their purpose, which is essentially to defend core provinces and lands from aircraft attack. For example, if I build nuclear rockets (for whatever reason), I will use rocket fighters patrolling around them overnight to keep them relatively safe from aircraft attack.
If you have any further questions feel free to say and we can discuss it 
