I have use Velcro for 5 years. I like it, keeps the armor nice and tight to the vest. The down side is having to sew all the Velcro to the vest. It takes a while and if you mess up you have to pull the stitches. But the good thing is if you mess up you can do it again, if you mess up with grommet you’re stuck with a hole.
On that note, I have never tried the grommet or the buttons so as for performance I can’t say. I’m getting a new vest soon and ill go back to the Velcro. That’s just my 2 cents.