I think you're think of James Hetfield, not Kirk Hammet. Mustaine wouldn't have anything to offer Kirk Hammet from a guitar perspective. I've seen both and I disagree but it's all good. You like what you like. Don't get me wrong, I like Slayer a lot but they don't have the depth musically that Metallica does. Dave Mustaine went to Megadeth after Metallica and they were okay but took a while until they started producing some decent albums.