This API module currently hardcodes boolean values as empty strings, e.g.:

$entry['enabled'] = '';

These should be replaced with actual boolean values, so that the empty string is returned in formatversion=1 and true is returned in formatversion=2:

$entry['enabled'] = true;

Additionally, since this would be a minor breaking change, we could also return an array instead of an imploded string for the actions property:

$entry['actions'] = $filter->getActionsNames();

As long as we notify users of the change via User-notice, I think this is worthwhile from the perspective of making the API module more future-proof.