If you want to have a healthy dog, do not let him off lead anywhere until his recall is solid in a safe place, ie. fenced yard.
You will be sorry for the rest of his life if he gets smooshed by a car and has a crippling injury. Some things you cannot take back. Keep your dog safe. He is not ready to be off lead yet. He MAY NEVER be ready. But giving him too much freedom, too soon, is a sure way to have a catastrophe.
I train come on lead. I NEVER use come off lead unless I can enforce it, until the dog is solid with the command. I train it with distractions too. If you let the dog win, either by not coming and doing what he wants, or by getting you to chase him which is great fun, then you can develop a long term problem.
Recall is nothing to fool around with because it is a life-skill. So train, train, train off lead.
I see NO reason to add a shock collar to this.
I think you would do better to add very tasty treats in your pocket, roasted chicken, dried hot dogs, steak, cheese, high value treats like pieces of pig's ears. Whenever you tell your dog to come, and he comes praise him and give him and awesome treat. Eventually you can phase out the treats, by giving him one every other time, or for the quickest comes. And then you can phase them out completely.
Bear Cub, Hepsi-Pepsi
Cujo2, Karma Chameleon
Ramona the Pest, Kojak -- who loves you baby?
Tiny Tinnie, Susie's Uzzi, Kaiah -- The Baby Monster.