First and foremost, the Half Ironman Training Plans program should be real to you, and where you are in life.
If you’re not currently running 15 miles, cycling 70, and swimming for miles straight - you probably shouldn’t start with an 8-12 week program!
If your current fitness is to run a mile or two, enjoy cycling recklessly, and you may not have been swimming for a long time - you need to get an Ironman training program for about a year starting with short running, cycling, and easy swimming.
The key is to set your own goals, and to choose the program that you think you can really ‘do’ using - is an important step in that process