UPDATE: I’ve tested to see at what point the app stops saving new data. I have an outline that at a specific point, when I add new notes, will simply lose those notes as soon as the app is closed; upon reopening the app the outline is always at the state at which I’d previously began working. Saving the outline as OPML results in a 61 kb file; saving the outline as a PDF results in a document that is approximately 12.25 pages long. Anything more than this will not be saved by the app.
ORIGINAL REVIEW: Cloud Outliner 2 Pro has been relatively reliable for short outlines.
For long outlines on which I’ve worked, however, it has been extremely unreliable, frequently losing significant amounts of data from the end of the outline. This data loss occurs not only when syncing to other computers running the app and to my iPad Air 2, but even on the same computer on which the entries were made.
Another problem (albeit less significant) is that on longer outlines, when the number of entries reaches the bottom of the screen, the screen does not scroll as my typing goes onto the next line. This means that I cannot see what I’m typing, and therefore need to manually scroll down for each new line as I type (and, as another commenter mentioned, the app is extremely particular about where your cursor is when you scroll — attempting to scroll from the right side of the screen will frequently result in the screen not scrolling down).
I can recommend Cloud Outliner 2 Pro for brief outlines, but find it worthless for longer work.