I haven't had any TDI knife, but I've gone through their Handgun Levels I to III and can highly recommend them.
Even if you don't carry a knife, or plan to use a blade for defensive purposes, you should study how they are used so you can better plan how to defend against them.
As noted, you also aren't going to be picking your attacker, or the place and time of assault, etc. You'll get what gets thrown at you and there ain't no "do overs."
Empty hand, knife, stick, gun. Ideally, they should all blend together into a coherent fighting system.
The key word is "fight." Not "gun," or "knife," etc. Learn how to "FIGHT." With anything and everything.
Yep, it's kinda inconvenient. Until you need it!