I sent you an email in regards to the 2 units.
Start the pup sooner than later. By the time you start hunting him you won't have to use the collar, just put it on him. Although it's nice for any emergency stop such as a road coming up etc. if he is ignoring you for what ever reason. My dogs where one almost every time they go out.
My 3 1/2 yr old was started at about 2 months old. The 1 1/2 just started recently as I got her when she was a year old.
You just want to get them started by putting it on them and letting them just wear it for a while before you actually use it on them.