The blackout periods aren't great either. March 5-22nd and April 9-13th? So you've got half of January, February, and half of April with a few days in March (not many). I assume booking class K is available on routes that normally have no Tango fares?

Seems too restrictive to be very useful. Perhaps if they dropped the 7-day advance purchase requirement or the blackout dates, it would be worth picking up.