Thinking for a Change [TFAC] is a great introduction to the role of the Robot and how to work that process works.
Habit Hacking builds on what you learned in TFAC and provides an two five step frameworks for hacking the Robot and breaking and building habits. It's a more detailed and different approach than covered in Thinking for a Change.
For starters it's a video interview style rather than a workshop where Tom and Michael guide you through 30 modules on how to hack your habits. Also Habit Hacking is habit agnostic. It doesn't teach you a specific habit per se, but teaches you how to change (almost) any habit. So the emphasis is on habit change, building habit chains, leveraging tools for habit change, etc., introducing explicit patterns for change, much more than the scope covered by Thinking for a Change. However both training are complementary and bring something new and an important set of perspectives to behaviour change.
Habit Hacking shows you how to work with much greater precision and at the behaviour level than was possible to cover in TFAC. As someone who has been through TFAC, you'll be able to quickly build on what you've started there and target specific habits you'd like to break/form and then follow the step-by-step program and additional strategies taught inside Habit Hacking to do so.
We hope this will help you in making an informed decision as to what course/program best fit your needs right now.