Block Element is a new Addition to the Elements module.
Currently it can only display static content.
For dynamic content eg. automatic post title and featured images you will need to use the Header Element today.
Future updates to GP Premium and GB Pro will allow you to create Dynamic Content.
So to answer your question – if you’re happy with your current Page header designs and are happy with the HTML and Template tags you’re using then I would migrate them to Header Elements.
If you’re thinking of redesigning the content and you think GB Blocks will make that easier then i may wait a month or two for the updated versions.