We use Training Peaks exclusively for all our coaching and the stick plans we sell. We pay them a hefty for the ability to do that. When we wrote TftUA we didn’t want to force people into using TP. We didn’t want to come across as promoting TP since we’d get nothing from them. We wanted the book to be a stand alone guide. We’ve used our grading system for a long time before we started using TP 5 years ago. It’s simple and effective. The TP one is also good. Use the one you feel is best for you.
There’s nothing magic about either.