I will let Brooks go off leash in appropriate places. His recall is 99.99% reliable under pretty much any circumstance. That being said, I do put an e-collar on him when he is off leash in public areas, but I can't remember the last time I had to nick him when I called him. I also have the whistle I use when we are field training on me when I have him off leash. He has been trained to immediately sit on a single whistle blast, which we mostly doing blind retrieves. I also do this randomly when were are just walking in the woods when he's off leash. He will sit until I call him to me, or I release him from his sit.
On the other hand, Sophie will never be allowed off leash, as her recall is pretty much non-existent, despite years of training. I'm pretty sure it's inherited, as there are 4 other dogs from her litter that I stay in contact with, and they are exactly the same. NO recall. I will let her run with a 25' check cord in isolated areas, letting her drag it along.
How old is Diggity now? How are you practicing recall in the yard? How do you enforce the command if he choses to ignore you? Have you tried letting him drag a long check cord while you are out of the yard???
One of the keys to any obedience that I have learned is once they have learned what a command means, and what you expect, you only give it once, and of it's ignored you enforce it. When I was training recall with Brooks, and I was fully certain he knew what I expected when I said "HERE", I would take him various places around the neighborhood with him wearing a collar and a 15' lightweight para cord dragging the ground. As he was wondering around, I'd randomly call him, if he came to me, it was party time and a treat. If he didn't immediately come to me, I'd pick up the cord, give him a tug and repeat "HERE". When he got to me it was a party and a treat. Every, Single. Time. Never scolded them when they come to you, no matter how baldy they may have ignored you. Coming to you has to be the BEST thing that ever happened to them.
Realistically if I wasn't in public areas with traffic close by, I wouldn't hesitate to let Brooks off leash without the e-collar. For us, it's basically the emergency back-up just in case.