^This is the perfect answer to this thread^Personally, it depends more on the matchup. I want to vortex characters like Martian and Batman alot because Sinestro loses to them in the neutral game. But there are other characters like Catwoman and Green Lantern where you are better served by putting them full screen and building the trait so that you can have an easier time when they do get in.
As for the vortex being reactable. . . That opens up a whole other conversation about what it means for something to be reactable. This varies from person to person and situation. Generally speaking, no Sinestro's vortex is not "reactable"
And as already stated if you try to fuzzy guard it then the Sinestro player can just change his timing