Lancer Zero Hecarim hype. Actually jk. There's probably like a 2% chance that you get that skin shard out of a Mega Orb.
https://thumbs.gfycat.com/IdenticalFirstBats-size_restricted.gif
I don't personally see a point in the Mega orbs, considering how low your odds at getting the new skin will be anyway. I think on average a regular skin shard is actually worth more than a legacy shard.