If you show up with your Private certificate, you will still have to refly their private program, but you will not need an FAA checkride for the rating to continue into the IFR program. You will be flying a complex and high performance aircraft. You will need both of these endorsements before you can solo those planes. They are also teaching to their standards, and at the completion of the private program, you need to be at the same level as the pilots who had no previous hours. This is quality control on Mesa's part. Just because a pilot holds a Private, or even Instrument rating, that does not mean that they have the skills necessary to perform to the standards that Mesa expects of its students. The only way to guarantee that each pilot is at the required skill level at the completion of the program is to have each pilot complete the entire program, regardless of the previous flight experience that the pilot has. If you are contemplating getting your pilot certificate to reduce your expenses at Mesa, it could work in the exact opposite way if you learned some bad habits that they have to break you of. That only takes time in the air to unlearn, and time is money. If you have previous flight experience, great. Go to Mesa to learn how to fly as a career pilot. I don't believe that previous flight time has an effect in either a good or bad way on your acceptance into the program. If you can start the program with zero time, and not spend extra money beforehand on unnecessary flight training, that is probably the way to go. If you already have some ratings, realize there will be some duplication of effort and expenditure. Fly Safe