Is ecm tuning worth it?

[OKGMC4]

On a fairly stock 5.3 engine isn't there really only about 15hp difference? Or is there a lot that goes into the trans settings and under the peak hp that make a huge difference? It's hard for me to dump a bunch of cash into it when I'm not sure the change will be worth it. Mail in tunes like blackbear are cheaper but wouldn't be as accurate as a local guy that does it with a wide band...he wants $550 and says I will have to leave it for a week at his house, and that seems really excessive. I know the tune is critical if you have done serious mods but mine is basically stock except a custom air cleaner and free flowing exhaust. Has anyone done this and give a thumbs up or down?