The Mind Ball by David Regal is one of those effects that is fun to perform each and every time you
do it. What you see is what you get, so if the effect interests you pick it up. There are no hidden
draw backs. Just be aware that you cannot control when both cards will be revealed. But, to my mind
that makes it more fun, and entertaining as a performer because you have to roll with it. No pun
intended.
I think a great way of presenting this is to simply leave it in in plain sight
in one of the display boxes and wait for someone to ask why you carry a magic 8 ball in your magic
kit, explain to them it isn't a magic 8 ball, but a Mind Ball! then ask them to gather some people
for a demonstration. It makes an awesome soft opening to a show, especially at a wedding or banquet.
Let the person that asked gather some friends, perform Mind Ball, then tell them the main show
starts in 15 minutes. They will go out and drag an audience back to you via word of mouth.