2015 Leaf Heroes of Baseball is only available in retail. Each blaster box comes with 20 packs and 1 Stan Musial autograph.
I did a bit of a double take when I saw "1 Stan Musial Autograph Per Box", given the fact that the product is from 2015 and he died in 2013. I went to scan the price of the box, figuring it would be priced at $75 or something ridiculous. It scanned at $40 which I figured was probably fair enough given the guaranteed hit. I didn't have a Musial in my collection so I figured I would give it a shot.
Here is one of the packs from the blaster box.
Much like in the Pete Rose set, the guaranteed hit doesn't come in one of the packs, it comes by itself in a toploader. Here is the one I got in my box.
The cards in the product aren't particularly exciting, there aren't any special parallels or anything, at least there aren't any that I came across.
My overall impression is... buy one if you see one. If you are a huge Musial fan maybe you can chase the autograph set or subset. If you are just an auto collector like me, its worth it to have the hit in your collection. But the cards in the set appear to be thrown together just to have some substance to go with the hit.