I can vouch for the Chill Portion model. We use it on cherries, to time Dormex applications, and it is by far the most accurate system out there for all flowering tree crops. Once you know your threshold number (the minimum Chill Portions needed to set a crop) you can predict the season and crop load pretty accurately. One other piece of advice, if you do use it is best to use a data logger in your own field than rely on the university or extension service numbers because local conditions vary a lot.