The whole point of using a ball machine in the first place is to transfer stroking skills into competitive play. If the balls used for the machine are dead, then players will get very good at timing and hitting dead balls. Unless users play their matches with dead balls then their practice sessions will have very limited value. It has been approved by the ITF for tournament play and is the first newly designed tennis ball in 30 years. While slightly heavier than regular balls it is much lighter than pressure less balls, and should be your first choice in choosing a long lasting ball.
Many facilities have a flow of slightly used balls from team play, round robins etc.
The problem with using these balls is that the life of a tennis ball is literally 3 to 4 weeks at best. Balls simply lose their air and fail to bounce well after that time. It is a chore to constantly cull out dead balls and to bring in fresh ones. This is the process many Pro's go through for their teaching cart balls, and it is a real pain. Even if done regularly the balls still have a significant variability and this is not optimal for machine use.