All three apps sync together pretty harmoniously.* However, there is some variation in the user interface between them. Some of this variation will be removed in OmniFocus 2. (But we might change the Mac app in other ways, and then the iPad app will be waiting to catch up.) If you want to take OmniFocus for Mac out for a test drive, you can download a free 2 week trial here: http://www.omnigroup.com/products/omnifocus
* If you make a lot of changes on one device and then switch to another, it's wise to sync the first device and then sync the second before making edits on the second to avoid a particular bug that can revert those changes.