it depends on who conducts them and how
Very true. In the Nimrod case, Mr Walker was firm but fair. He did not appreciate being lied to by MoD and allowed the families a certain leeway, such as producing the airworthiness regulations that MoD told him were "irrelevant". The Government response was to try to gag Coroners.
At the opposite end of the spectrum, at the Sea King ASaC inquest (Jan 2007) Sir Richard Curtis flatly refused to allow the father of one deceased airman to challenge blatant lies by MoD. In fact, all but shouted down the father in court. The MoD legal guy didn't even have to try, it was so obvious whose side the Coroner was on. It was HE who was adverserial!