So tennis is your thing? With the Slinger, you are going to have an easier time getting some good practice. It fits in a bag and lets you set your serve preferences to get a good warm up. You can change speed, angle, and other settings.
The Slinger has a max serve speed of 80mph. Its battery lasts up to 5 hours. It comes with simple dials to change speed and frequency. The bag has space for your towels and bottles too.