I would be reluctant to ever treat my home network as secure. I just don't have time or expertise to validate that. Instead I want my router to be maintained by someone responsible to try and mitigate threats. Google may not be perfect, but they are probably more competent than an ISP or companies like Linksys or Belkin. For Google to be able to update the firmware they need complete access to the system and they could certainly use that to invade my privacy. And the more you trust your home network the more that is a risk to you.