Cey is fairly reliable off-leash - but only when there's no dogs, people, or other interesting things walking by! Haha, even then he is generally reliable, though still not 100%. But we started very young. I think that THE most important thing when training for a reliable off-leash recall is to repeat it over and over, giving a VERY high-quality treat each time - AND THEN LETTING THEM GO BACK AND PLAY. Do this EVERY time you take them out for training for recall. Don't EVER (at least, not until they are much older/more experience/more trained) call them back to you and then restrain them in any way, at least as much as you can help it. From the very start, the recall should be associated 100% with a completely positive thing, and never with a negative (i.e., put on the leash, put back in the car, etc.) thing. If you for instance are at the dog park, make sure the last time you recall them is to maybe put a flexi-leash on them and then let them go play a little bit more, even following them around for a while, so that they absolutely do not associate the recall with any sort of negative experience (and yes, being restrained/taken away from the dog park is, for a dog, a negative experience lol!). When they get more used to associating the recall with a completely positive experience, you can start occasionally calling them to you and then restraining them. But even now, I still generally give a treat of some sort to Cey when he comes when called, even if it's just coming inside from the yard after a pee-break.
By the way, I still never let him off-leash in a busy area, let alone if there are cars around. I completely envy the people with dogs who can walk off-leash in situations like that, but I just could never do it with Cey... he is only off-leash in very limited areas where I am fairly certain he won't run into a street and get run over or anything if there's another dog he sees...
But I do let him off-leash on the beach, or in the (unfenced) front yard, or occasionally when for instance I take my daughter to soccer practice and I'm letting him out of the car to go run around and there is plenty of grassy space for him to run without too many other distractions around. As I said, he does pretty well - not 100%, but he is reliable enough in those situations that I am confident that he would return to me if need be. (I still usually take at least one or two nibbles of cheese with me however, and mix those up with his more boring treats, and call him to me and give him treats and then let him go, to remind him of the wonderful things he could get from listening to me hahahaha! -In other words, I don't think that the recall training ever really completely ends