In reply to trevellyan.

Actually, the original, Legacy Theme Options interface won't go away - it does require adding a plugin, but it is only used when the admin is opened. I know some people still prefer that method. And the Weaver Xtreme Legacy Theme Options interface was the result of plenty of experience and feedback. And because I know it so well, I do use it myself for tweaks to existing sites. But I'm working on a new site, and I'm finding the Customizer version much better for doing new layouts.

As always, my own philosophy is to provide a tool that works the way the user wants - all the options needed, and whatever interface is preferred.