I know this wasn't for me, but my friend has watched all of Rattler's games in college and is a huge fan of his. Rattler can get to top speed super quickly, but he doesn't have top end speed at all. So overall he's slow, but he's really quick too. I'm guessing he's thinking and thinking slows you down.
He's got what I like to call phone booth quickness. He can make defenders miss in short areas, and if he recognizes the rush and triggers to run quickly he can get a quick 7-10 yards, but yes you're right, he's not a top end speed guy.