.
Short answer: No
Long answer:
The main issue with transferring all content between various CCK components is the custom fields are, well, custom. This creates many different data structures so a simple one-fits-all transfer/import solution is not possible (or certainly not easy).
Some options . . .
Manual Database Transfer:
K2 stores the content in its own tables (not com_content tables like FLEXIcontent).
So you may be able to use phpMyAdmin (or similar database tool) to selectively export the data from the K2 tables and then import that data into the Joomla core jos_content table, and then import that content into FLEXIcontent like any other core content.
RSS Feed into Core Content:
The K2 component does have RSS feeds which can be imported into Joomla core articles using a component such as
FeedGator
.
FeedGator imports RSS feeds and converts them to core articles.
The K2 feeds on your own website can be fed into FeedGator and converted to core content articles.
Then import these articles into FLEXIcontent like any other core articles.
One of the major advantages of using FLEXIcontent is you are not stuck in an incompatible component and can go back to core content much more easily if you so desire.
.