Ok I had to look this up 'cause some things didn't sound right and didn't want to just keep doing the "from what I remember" game.
According to WoW wiki:
http://www.wowwiki.com/Heirloom
"
Heirlooms can be enchanted only with enhancements that will not bind the item to the character. The items are treated as item level 1, and so most Burning Crusade or higher enhancements cannot be applied to them. Death Knight runes became applicable to heirlooms in 4.0.1. Enhancements that require a base character level to use, such as Zandalar Signets, will become active only when the character has reached that required level."
So it shouldn't make them bound to the character, 'cause those enchants won't work.
but ya it's only good if you're doing pre BC levels since they have to be lvl 1 enchants.