The hard part about buying a ball machine is that it is almost impossible to test it out before buying. What I've found is:
1) Spin is essential. Without spin, the machine is virtually worthless
2) Once you use the topspin feature, the ball speed slows down A LOT. Making most machines worthless.
3) Don't spend extra for the fancy "players features" that are supposed to replicate "actual match play". They don't. Ball machines can't replicate match play. All you are doing with a ball machine is grooving basic strokes.
- For example, I have an old MatchMate (big club machine from the 1980's). It's great. It's like a DIY version of a Playmate. Using topspin, the balls come plenty fast. Underspin is virtually worthless. The underspin ball delivered is nothing like any kind of ball a human would ever hit. And it's nearly impossible to have it hit make it over the net and hit the court. At least with much speed.
- I've also used Tennis Tutor portable battery machines. The ones without spin are basically worthless. Yes, the balls can come fast, but if you have it at top speed without any spin, you can't hit the court with the feed. It sends it into the back fence at top speed. It's also a very unrealistic feed.
- The Tennis Tutor with spin (I used the Model 4) is worthless. Once you add spin, the ball comes out too slow. Painfully slow.
- I've hit off the "Slinger". It's like a carnival toy or something. The weird spin it produces is nothing even close to what any human has ever hit. I can't believe they've sold a single one.
I guess my advice to you would be, even though it is really hard, try to some way test out any machine before you buy it. And plan on spending more than $1,000 for one you actually want.