I'm not a huge fan of hitting aids I never wanted to spend the money on a gimmick that might not work. However, the two things that I did often was train with different size balls off the tee and front toss. I would also use a thing called the swing rope and hit tennis balls with it off the tee and front toss. I found the swing rope to be beneficial at keeping the hands back and the different size balls helped my hand eye coordination.
Did anybody ever buy a hitting aid that helped or was it a waste of money????