The times I’ve used them, the original bill was so outrageous I fumed for days.
Insurance paid ~$15K and they billed me for my entire OOP max for the year ($7,500) for a service that cost about $400 tops to provide.
Contested the bill and they do a medical review of the coding. They had billed as “intensive care” the administration of a single shot and a standard blood count.
They actually came back and claimed the coding was correct! Kept fighting it for about 6 months and they ended up dropping the entire thing at no cost. But they still got to keep the insurance payout.
Just another form of price gouging / variable pricing which should be illegal.