Flak jacket helps with pieces of glass that would normally puncture in 1 go. An armadillo might hold off for many pieces of glass. The rubber compound used in my armadillo tires seem to fend off glass getting stuck in there. Like it's more resilient and doesn't allow glass to "sink" into it though I do end up picking 10-15 pieces out each month.

Keep in mind though, if you get a piece stuck in there and it consistently grinds it's way through the threading, nothing will keep you from getting a flat.

I've noticed though that the armadillo's feel about 25% less "lively", it feels like I'm riding on flat tires even though they're not flat and pumped to the max PSI. The ride feels more sluggish to me but hey, they're only on my commuter bike.