I think transparency is a good thing, of course, but I don't see this particular change doing much to lower costs. As has been pointed out, the vast majority of health care transactions are between the provider and an insurer, and they negotiate their prices outside the chargemaster.
In my opinion, a much more consequential change would be eliminating the ACA requirement that insurance companies spend 80% of the money they collect on care, and use the other 20% for all of their costs (including their profit). While the rule was well-intentioned, it takes away the insurance company's incentive to negotiate lower prices, because they have to refund the savings to consumers instead of keeping it to boost their profits. On the other hand, if the providers raise their prices and the insurer has to pay out more than 80% of their revenue, the insurer can raise its prices to keep up. And it gets to keep 20% of the higher price. So the only way they get to make more money is to increase their total revenue, which can only be done by letting providers raise their prices. Seems like a textbook case of unintended consequences.