For greater accuracy, consistency, and durability, we advise you to use pressure-less tennis balls with your tennis ball machine. We usually recommend using HEAD TRAINER, Wilson trainer, or Dunlop Coaching balls.
You may also train with pressurized tennis balls, but they won't last as long as pressureless balls. This will result in higher costs as you will need to replace them more often. Shall you prefer that option, the HEAD TOUR XT is great option.
Last but not least, Slinger and all Lobster Sports tennis ball machines are compatible with kids balls (which are typically green or orange colour), red and yellow/red ones excepted.
Note that due the ever-changing and broad variety of tennis ball brands or types, it is impossible to keep track of those that may or may not be compatible and offer optimal results with your machine.
We would strongly advise you to contact the manufacturers directly to enquire about that.