Comment 13 for bug 871325

This statement asserts that libunity is preferred over the DBus interface:
"While the libunity API is stable, the DBus protocol underneath is not. We strongly discourage anyone from relying on it."

If libunity ends up changing, we can expect the soname to change, and so the worst that will happen is that Gecko will fail to find the library and will fall back to current behavior. Even then, it probably won't be too difficult to adjust Gecko for changes in the libunity API. So using libunity sounds fine.