It's only the right way to do it from an application developer's perspective if the behaviour of the official OS-approved interface matches what their application needs, which is unlikely to be the case here. For example, according to https://support.microsoft.com/en-us/kb/156932 there's a fixed-sized pool of threads used to fetch data into cache to fill async I/O requests. If you try to have too many async I/O requests for the number of threads (which can be as small as 3) the excess are automatically converted into synchronous, blocking requests. This renders the API useless for something like an event-driven web server, because any file I/O call could block the main thread until it completes.

(Also, curiously when the data's in the cache that page shows a performance penalty for async reads that complete synchronously from the cache compared to sync reads. Wonder why.)