It depends on:
* One's sailing experience, both in general and on the boat in question
* A frank self-assessment of one's abilities
* Where the boat will be used and under what conditions
* What risks one is willing to take
* Past experiences with safety practices that have and haven't worked
* Military background, if any -- I'm sure this develops a better mindset to plan for *and* handle emergencies.
* Recommendations from others
* And many other factors
My advice is NOT to be fastened by anykind of seatbelt.
But to fastened to the kayak.
If you by ANY chance will fall overboard, your ONLY chance is to stay with your kayak. So you must secure that you will NOT be separated from kayak.
The TI is very stable so if overturned you will be sitting under water trying to get your seatbelt OFF. And when it is OFF you don´t have any secure connection to your kayak. Better having a connection with your kayak that feels ok when you are swimming in the water. Sorry for the bad english, but I think you get my point.
regards from Sweden