I have two 66% pos hets so you know what my answer is gonna be.
It depends on somethings. Are you a casual hobby breeder doing this for the heck of it? If you are sure go for it. How big of pied project are you shooting for? These are just some questions I ask myself reading the title of this tread. If you or any one is starting a pied project I don't think adding one or two pos hets is a terrible idea. But I should mention I bough my mystic potion pos het kinda just for the heck of it. And I bought my super pastel pos het puzzle cause I believe he is 100% het for puzzle based on what I believe is puzzle influence in his pattern. So I got the super pastel to save money basically at the time and feel I got a deal oh him actually.