I've got a love/hate relationship with PMs. I road with one for 1.5 years, and it got to the point that even without looking I could tell a 10w difference and I figured out how to correctly pace myself within a certain zone for a certain duration. Did it help me for the 1.5 years? Absolutely.

But it had diminishing returns; I'm the type of rider that will focus on training data so much that I'm no longer having ANY fun while riding (fun?! gasp) So I sold the PT, got a bunch of money in my pocket for schoolbooks, and now use the knowledge I gained in a year and a half to apply it to my current riding. And my best results of the season were AFTER I sold the PT!