Thanks for the feedback about the title, I'll ensure the title gets a better name. I'm thinking of ditching the question for a statement -- as it is the Welcome program -- "A desktop for everyone's tastes".
The text underneath will be amended to:
Ubuntu MATE holds a wide range of customisation options, including the ability to offer a layout that is familiar towards your workflow. You can choose one as a starting point and make further changes to it later.
This should hopefully provide the hint to new MATE users that these are not "fixed" options and that it's possible to configure panels and applets later.
Definitely a typo
On my (relatively clean) VM of the 18.04 daily build, panels have been switching without a problem. There were only minor quirks like all windows minimising (usually when switching between dock-based panels).
This feature literally executes MATE Tweak, so you could see if switching panels works OK there normally.
Clicking a panel will apply it straight away, so I'm not sure on a delay timer/revert option in addition.