I haven't used a slip bag before but it's the same concept in some ways. By using the swing of the bag. This is my next challenge but with kung fu but punching the target .
Currently I use a bell on a rope to train my defense, blocks and cover and striking in between the swing. In order to reach the target on the other side.
Right now the only thing I'm hitting is a tennis ball. I want to eventually be able to strike a pool ball or a lacrosse ball but I'm far from that. Then for tiger claw techniques I will use things like sand, beans or a swim noodle depending on what technique I'm training.
But at the moment the tennis ball is killing me when I strike it in the wrong area of my fist. It just hits the same spot over and over and after an hour I start to feel it. The tennis ball is safe and a good beginning point for me when I train my knuckle punches as well. I have 2 that I can actually use, but one is my favorite.
As for the difference? Yep, after 2 days (1.5 hours each day), I've notice that I'm more relaxed and my strikes are really fast compared to where I was even when I was training for competition. My accuracy is much better and I'm now training my son on it too. His first try he kept hitting the tennis ball to hard and he couldn't control the direction of how the ball would swing. If too much force hits the right side of the ball the ball will swing left. This instantly made it easy for me to see without video that was swiping his jab. His timing was also off and his arms got tired lol. He couldn't do the back fist one, but the straight jab he was able to do. I'll try to get some before and after video of us so that others can see what improvements are visible. But for me I know I can tell that my speed has increased it shows in my forms.