I know that the armored egg is for stat boosts, but I don't want to accidentally waste it. The item gives me both eat and use options, which one gives the stat boost?

The use option. Click it then select your pet and confirm. The eggs are only useful until t3. I also fed one of each to my foodie pet.

just wanted to make sure, thank you!

Welcome! Good luck with training! Don't forget the battle forum if you get stuck or want advice.

The vast majority of time when there are more than one options (some items have more than two) and one of them is 'eat', eating the item will be using the item like food and won't do anything but make your pet less hungry.