The argument against this is that other external-to-Google-but-started-by-Google projects like Golang and Android use the multirepo model, with gerrit.
There are pros and cons to each - do you want to have a hugely churning "I always have to rebase/merge" repo under you, or multiple repos and trouble keeping them in sync?
Having done both, I'm not sure which is better - it's probably very project specific.
Android uses multirepo model not because they want to, it's because they have to. You can't have a single repo Android's size in git and still run it snappy. All the tools, including the old repo tool and the new toolings around gerrit, are to make the actual multirepo model works like a single repo.
There are pros and cons to each - do you want to have a hugely churning "I always have to rebase/merge" repo under you, or multiple repos and trouble keeping them in sync?
Having done both, I'm not sure which is better - it's probably very project specific.