i havn't used those on my mustang, but i had the same thing on my audi a4 and loved them. those look really good, i may buy some too. on my audi i couldn't get the clear cover off so i had to fit the trim rings from behind the gauges, made it diffiuclt, and i spilled a little drop of glue on the clear, but i think the mustang besel comes completely apart so you can lay the trim down from the top
I have similar ones to those, I forget where I got them, they were off some random website that only sold them i think. I got them in brushed to match the accents on my bullitt.