I've worked with a couple of halfies and they're both characters. One is a cross with a morgan that I ride every now and then. She can be very stubborn and needs someone who won't let her get away with her tricks. She's bolted with me once when a school bus came barreling over a hill much faster than it should have. However, that being said, I was riding her when a large tree fell down in the path behind is and she barely spooked. That happened on two occasions and both times it scared me more than her. She's also a pain to catch, but will give you a really good ride. She really is steady on her feet and can handle harder terrain better than other horses in the barn.
The other halfie is a therapeutic riding horse. He's also very stubborn and is starting to get too grouchy for the program. The instructor is trying to find another pony to replace him so he can be sold. He'd make a good 4-h horse with the right rider. He's just getting to hard to deal with when there are kids who are trying to develop their balance on him.
Do you have an arena you can ride in? It might help you build confidence on him if you have someplace he won't bolt where you can also figure out what you need to do to keep him going how you want.