Springs in heat exchange tubes - your thoughts?

About two years ago, on this forum, there were threads regarding using springs in the heat exchange tubes. The purpose was to increase the heat output. I am interested in your experience with the springs after 2 years of using them? Are you still using them? Is the air flow restricted? Do you believe your air flow temp's have increased? Thanks

The thread is here:
http://www.hearth.com/talk/threads/quadrafire-castile-experiment.58216/
Its 8 pages include some updates from this season.

Thanks for looking that up, Swineflue. That should answer most questions. Mine are still in there doing what they did two years ago > less heat up flue means more heat into the room. It would make no sense to go back. I only wish that there were a way to create more surface area on the outside of the tubes to absorb more heat.