The Spark is meant to be used with the VivoKey platform. Of course you can use the UID with compatible 3rd party access readers and things like that, but the Spark is about linking your VivoKey profile to you securely.
The Flex One will also have a VivoKey Identity Applet installed for this same purpose, as well as the ability to run autonomous java card applets. That said, I will definitely keep my Spark and my Flex One prototype… no reason to not use both really.