I had a friend of mine serve tennis balls at me. He was a pretty good player and hit me in the head a fair bit, it's quite a fun exercise to be honest. That being said you do have carefull with this as tennis ball can get through between a grill and peak!! It will make you're eyes water!
I love the sound of this! Sounds like a Woolmer-esque training method.
Perhaps to really get your eye in you could ask a golfer to drive some balls at you from 22 yards.
As someone who prefers the ball the faster and shorter it comes my advice is -
1. Fear should not cross your mind. Get a lid on and be prepared to wear a few sometimes, No one has ever died from a bruised chest/arms. If you want proof of this YouTube 'Brian Close'.
2. Certainly at the levels I've played at, you almost always have more time than you think. That said, stay with the shot and Get a feeling for the technique, this is where the bowling machine is good. Do not use the short ball as an excuse for a wild thrash
3. Always watch the ball as far onto the bat as possible. You stand a much better chance of hitting the ball, or avoiding it if that is your intention, with your eyes open.
Best of luck!