They are great feeders, but just know that as babies, they can a lot of them.
They are also a bit more expensive than crickets, but I think they are worth the price and more thanks to being so much easier to manage and because they are so nutritious. No calcium powder needed, no need to gut load, etc.. They are also soft-bodied, so you can have a bit more leniency on the space-between-the-eyes rule. I would recommend you only put a few in their bowl at a time because they have a tendency to just swallow them, and then you'll find whole worms undigested in their stool.
I would buy a container and let them try them for a few days. You don't want to buy a massive quantity that goes to waste if your beardie is not interested. My first beardie went absolutely crazy for them her entire life. If I even knocked the container with my hand she would be up against the glass. My current beardie (Tuco) could not care less. He barely acknowledges them when I put them in his bowl.
As for a number...if they're gonna be your staple feeder, I think a normal baby beardie could 30-50 a day, and even more if they're particularly hungry.