> no author of an accepted paper will be denied publication due to lack of funds
Most APC-charging journals (like the Nature family) have a weaker waiver policy, where they only promise waivers to authors from developing countries, and say they may consider others "on a case-by-case basis" but with no guarantees.
Not to say that $1700 (roughly the number they list in their FAQ) is an unreasonable amount given the work that goes into reviewing, editing, and publishing an article. Indeed, I wonder if they couldn't raise the cost a bit.
Net effect could swing either way.
If you summarize the cash flow, the publishing industry charges twice the taxpayers in addition to the science worker and research institutions costs. If you want to make your article open access, then you pay extra fees and nowadays, the university funds ripped off twice: they still bear the cost of pay-wall publishers and open access. Long story short, the whole system is rigged in favor of gatekeepers. You may check this video[1]
The work reviewing and editing is unpaid. The entire cost goes toward publishing.