- A few dollars.
- I've been disabling a few tools and a few widgets each new version. Usually different set each time, I update the version.
- Name & Icon
- Future proof. I might change some things in the future, either disabling some awesome new features when I think they exist. Or simply not disabling anything at all. In either case the main version wouldn't be affected by anything decided whereas the free version might be. For example, discussions of in app purchases or whatnot might apply to adding features to the free version, but any such things would be added to the main version without any purchases. I'm not currently planning on anything of the sort, but in the future I might.
The intent of the free version is largely to get some feedback on the product what is like what isn't liked, and to help find bugs with a larger pool of people trying the app. So there really isn't much of a difference at all as that would largely undermine the purpose. I've seriously considered even not even disabling a few of the tools. Which would effectively cause no difference at all between the two, save icon and price. I use to lag the free version and update it less often than the main version, but that lead to reports of bugs that were fixed in the main version and undermined the goal of useful feedback and better bug reporting.