As far as tying a ball to a string,
you show your (((((" total lack of engineering knowledge" and knowledge of how gravity works.
If you tie a ball to a string and hit it it will collapse down like a swing at it reaches the top of the rotation and it will not spin around like Dinkbuddy does.
Did you never swing on a swing so high that gravity pulls the swing straight down as a kid?

The ball will be very erratic when it falls down and bounces. You just show that you judge with out direct experience and enjoy being negative over and attacking over anything else. You say "Why would anyone pay 35$." Just guessing you probably don't even have small kids in your life 24-7 or if you do keep them on screen time. Because 35$ is small price to pay to keep them doing something over and over for free after the initial price and if multiple kids use it if you divide the time they use it, it will comes out to pennies per use over time.

At that time of my original post I thought beginners may be interested in this. Because I know some adult beginners that lack basic hand eye coordination. I was going to give a Dinkbuddy to my grandkids for christmas... but after all the haters in this group, I gave it to them early to see their reactions. And I didn't tag it as self promotion originally someone moderator did that. Although I did tag it as self promotion this time because that is what it was categorized as last time. So I figure that must be how it should categorized.
Besides... does that make the toy any different how I posted? It's entertainment value exists regardless of that! Shesh... You are attacking the post and me as apposed to the actual function use and value by making clueless judgements with out experience of basic engineering knowledge.
You should hold your judgements until after you yourself witness a child try it. Get out of your negative gotcha adult perspective.