I've always used the Estes launch controller. I could never be sure the batteries had enough juice to ignite the motor. I saw the Pratt Hobbies launch controller (Sirius Rocketry I think) and it was one of the best decisions I ever made! I use my lawn tractor battery and it's a guaranteed launch every time! I absolutely LOVE it!

If you've ever wondered about it, don't even think about it! Just do it!