However, I'd argue that the use of open source firmware in this case is a means to an end, since proprietary firmware generally sucks. But since this is an article about how to have a quality Internet connection, rather than how to get started in router OS development, it might be more than suitable for many of his readers.
FTA: (...) a combination of commodity hardware and open-source firmware.
It's OK that you suggest RouterOS, I'm just saying OP is not supposed to mention it.