I have confidence in Marco that he wouldn't restrict players to have the ability to play without fps stutter. I have already said I am using it on realm, so it would be unfortunate if I am wrong about this... I do not see any reason why this would not be allowed. But I am not Marco, I am going to run the risk though.
60 fps pc master race.
Edit: Asked Marco in the shoutbox about this. He said as long as what it say's it does, is all it does, then he doesn't see why it could be a issue to use on realm. aka it's realm safe. As long as theres no hidden side-effects.