Ionic's widgets aren't web components and aren't usable outside of Ionic/AngularJS. This means they're not recognized as custom elements by the browser (no future dev tools support). They leak DOM and CSS internals into the page. Worse, they require the host application to be Angular based.

Brick components are encapsulated, both with shadow DOM and scoped CSS, and usable in any web page and with any or no framework. You can freely mix Brick, Polymer, Bosonic, or "raw" custom elements in a single page.

edit: It looks like Mozilla is dropping X-Tag in favor of "vanilla" (what I called "raw") standard web components APIs. This would make Brick a collection of components, rather than a web component helper library like Polymer, and more akin the to Polymer project's Paper Elements.