I really like the Dataflow programming model, but this feels to me like an apples-to-oranges comparison.

Spark Streaming is a fully open-source project; although the Dataflow SDK is also OSS, my understanding is that the released version can only handle bounded datasets. Support for streaming (which is the major innovation, IMO) is only available in the form of stubs that call out to Google's paid, proprietary Dataflow service.

It's totally fine to compare an open-source project with a proprietary alternative, but I think it's odd that this article opens by talking about how the Dataflow SDK is being opened, and then spends all its time talking about proprietary features.