Bottled faeries grant your pet certain battledome abilities, depending on your pet's level. More info on that can be found here:
http://www.neopets.com/ability_info.phtml
Whether or not you should use them is up to you. If you like to battle, and your pet is well-trained, then you might want to have the abilities. If battling doesn't interest you much and you'd rather have the neopoints, go ahead and sell them.
Congrats, by the way.