We just tested* a legal LLM and at least about 1 3rd of the cases it returned were not relevant to the question or the cases did not exist.
I tested it filing in citations only and it seemed to do that reasonably well but it still got two wrong. This was just looking up the actual citations of a case with a given name.
(Edit: *I should clarify that this thing came bundled in another service we already have. So this is not a service we sought out. It was shoved into my face.)