Always fine to add to a thread.

FAI is caused by deformities in the femur, hip socket or a combination of both. So there is more impacting the situation.
With a change in structure, it will be an ongoing situation that is monitored and needs work to be completed.

Are you working up/downstream to maintain the best possible positioning given your constraints of FAI?

Why does your physio believe it is making the hips less stable?
Has your physio offered other recommendations or ways to address this situation?

Have you considered pros/cons of surgery?
In some situations, there is no avoiding it.

I don’t think the true question is “Is banded distraction a cheap and temporary fix or has it got more potential than that?”
In what context(s) is this question being asked?
Banded distraction may or may not be the most effective solution or approach to what you are looking to impact/ your situation.
There is no one size fits all way to address any situation.
There are multiple paths to the same goals.

Does this help?