In reply to dgwyer.

I'm curious too. I've never had a theme user tell me they didn't like the Customizer. It's essentially the same things as the old "Options Panels" that nearly every theme had been doing, but with a live preview. It's nice to see changes before setting them live.

The usefulness of the feature is hugely dependent on the theme, though. I would assume these users experienced a theme's poor implementation of the Customizer. I can imagine a broken Customizer being quite bad!