I really like that paying up to DTAG is not the default and is more bureaucratic. This might already be enough to kill the ISPs' profiteering schemes, similiar to what happened with the Leistungsschutzrecht (see https://en.wikipedia.org/wiki/Ancillary_copyright_for_press_...) in Germany.
Since we cannot change market dynamics, we are offering our customers a way to offer their customers faster service during peak periods with this "pay per peering" option. ===
My understanding (which may be incorrect) is that Hetnzer is telling existing customers that instead of having to install servers within the ISP network, they can instead pay a marginal fee per month to bypass the congested peering links to these providers.
I think the name "double paid traffic" is a very clear statement. They are not trying to sugarcoat this or anything. They just don't want to loose customers over this.