A backend model should always be a \Magento\Framework\Model\AbstractModel

dmitrii_fediuk (Dmitrii Fediuk) January 11, 2016, 12:45pm 2

See also:

What is the backend_model for a backend configuration’s form field?
A frontend model should always be a \Magento\Framework\View\Element\AbstractBlock
Logical error: Magento 2 checks whether a backend config form field’s «backend_model» implements the \Magento\Framework\App\Config\ValueInterface interface only, but actually calls the «backend_model» for much more methods (absent in the interface)