One of the problems with these systems - maybe they've solved it by now? - is that they bundle up virtually everything for a running system, including the GUI - so any custom theme you have outside of the "package" doesn't translate over.

There are other downsides, too.

At the same time, the upsides of such systems are really nice; they are very much reminiscent of MacOS apps - and that I really like. If the whole theming and such can be fixed - it would be perfect.