Originally Posted by Chotobaka
If you actually are 3.5-4.0 this is absolutely useless.
Disagree. I had bought one of those cheap twist ball machines machines some 20 years ago when I was at that level. I believe that it cost me less than $70 at the time. I did find it useful at that time for groundies and volleys. I was also able to elevate the machine (with a flat-top garbage can) to work on my overheads.
Later, in the mid/late-90s I would sometimes use it with my students.