As usual, Walt Mossberg gets to the heart of the matter. Here he is on the significance of the “Facebook phone”:

In effect, Facebook has created its own phone without having to build or sell hardware. The HTC First, so far the sole phone on which it’s preloaded, even boots up with the Facebook logo.

I found Facebook Home to be easy to use, elegantly designed and addictive. Although I’m a regular Facebook user, I found that, with Home, I paid more attention than ever to my news feed, Liked items more often and used Facebook’s Messenger service more often. So, if you are a big Facebook fan, Facebook Home can be a big win.

But I found some downsides. Facebook Home blocks the one-step camera icon some Android phone makers place on their lock screen to allow you to take pictures without first unlocking the phone. It also overlays other lock-screen features some Android phone makers include, such as weather information or favorite app icons. And if you do go to the icon-filled home screen, you’ll find that Facebook Home has taken that over as well, topping the screen with a bar that makes posting to Facebook easier and eliminating the bottom bar of heavily used apps.

By default, the first of these Facebook Home app screens contains Facebook’s apps, including the popular Facebook-owned service, Instagram, plus apps from other companies, like Google GOOG +0.36% Maps and Google Search, and the camera app. You can remove these and add others.

With Home, Facebook is essentially staging a land grab of Android, the hugely successful mobile operating system made by one of its key rivals, Google. Facebook Home leaves all the standard Google apps in place and doesn’t alter the underlying Android operating system. But because it’s so dominant, it makes it less likely that a user with limited time will launch Google products that compete with Facebook, such as Google’s own social network, Google+, or rival services from other companies, such as Twitter.