In issue #27, it was asked if this middleware is the same as acdlite/redux-promise.
Both middleware solve the same problem, but the implementation is different. This middleware dispatches a pending action in addition to a rejected or fulfilled action. This is a feature acdlite/redux-promise has not implemented at time of writing (November 2015). The pending action enables optimistic updates and describes an unsettled promise.
Both middleware do use the Flux Standard Action specification.
One could also argue the API for this middleware is more transparent and easier to integrate, e.g., you do not need to use redux-actions.