I use JournalPress, which generally works very smoothly.

(The one exception is that a particular combination of starting a post, saving it as a draft, coming back to it, and doing something else I haven't identified yet leads to the cross-post button getting unchecked about half the time. However, that's easy to fix: I just moved the crosspost widget right near the publish button, and check it manually.)

But in general? It works.