I can imagine what he's like fan and totally get that it's a massive uphill struggle. Some of it will be immaturity, Oldgirl was a nightmare for the first couple of years, she had zero recall and pulled like a train, but did calm down eventually and ended up as a fantastic companion. I used to cringe out and about, because she looked exactly like those highly attentive, super motivated Border Collies, but behaved like a teenage hooligan. 
Essentially, what you are trying to achieve is counter conditioning him into automatically reacting to your cue, as you have made it soooo exciting at home in the house, then garden etc. So he wouldn't stop and think - "Oh yeah, but Mum only has that toy - whereas those are OTHER DOGS Whoopee!" The response would be a conditioned one, where he comes back to you without thinking and for that most of the groundwork is done at home in the house, then garden, then you'd longline him while gradually building up his response outside. If he fails at any point you'd go back a few steps and really ramp up that stage before moving on again. Tiny footsteps.
It is a huge undertaking and it really depends how much of a problem he is to you out on walks as to whether you feel you want/need to do it.
With the Total Recall, if he didn't respond when you dropped the high value treats, he wasn't ready to move on. Each stage can take massively different lengths of time to move on from, depending on dog/breed/personality.
Have added the Moose to my wishlist and will get it when dh isn't looking! 