TYPO3 Core

about \TYPO3\CMS\Core\Resource\Driver\DriverRegistry::registerDriverClass

FAL drivers are registered with their class name an optional short name and optional label and an optional configuration

about \TYPO3\CMS\Core\Resource\Driver\DriverRegistry::addDriversToTCA

This method builds the options for the driver selection of a sys_file_storage. The value of the select option is the short name. If the short name was not set when registering the driver class, the class name is used instead.
When calling this method twice (it's called once in the core), any previously added driver will get added another time, which leads to following html:

<select id="tceforms-select-56362d68cb05a591576089" name="data[sys_file_storage][4][driver]" [...] class="form-control form-control-adapt">
    <option value="Local" data-icon="">Local filesystem</option>
    <option value="Local" data-icon="" selected="selected">Local filesystem</option>
</select>

To prevent confusion of editors/integrators, any option should only be displayed once, if they have the same impact.
addDriversToTCA should therefor use the short name as index for the options.