The Pandora gem is way better and will be used way more, your timer starts as soon as you hit that launcher so you're 30% extra damage is going to be horrible scaled due to Cross Rush, normal, special, switch cancel than you start the 30% extra part. That or you do a Launcher normal special raw tag and than you have to open someone up in the next 8 seconds.
Pandora gem makes a 600 dmg combo into 780, from the looks of it over half the cast can ex wallbounce into pandora. You'll be seeing ex wallbounce into Pandora with this gem for sure once the game is a few weeks old. It's still a risk though, since you're leaving a sub 25% health character out trying to combo into Pandora.