Once you own an heirloom all your characters can use it. They are in your collections tab in game. Heirloom Basics Heirlooms provide experience boosts and level up with the character. The rest of the guide focuses on not having that friend.
If farming this gear is more time consuming/too expensive to you than leveling without this stuff, then play on, but a few tips might help you grab some pieces without taking too much of your time. Refer-A-Friend (let me know if this link ever dies) is the fastest way to level up alts by playing with who you referred without paying money. Although you do get one level 90 boost purchasing the Warlords of Draenor expansion, and a level 100 boost with Legion.
Preparation Basic Boosts Buying level 90/100 boosts is now the fastest way to level up, but it's expensive (for most of us). I'm hoping that this guide helps to collect herilooms in a timely manner so that their collection does not take more time than to level without them. I will include extra information for those who aren't going for straight fast/cheap leveling. Remember this is for fast/cheap, not perfection. Thanks for all the feedback, and keep it coming! If you want to be able to try out every class at max level, or level up several alts so you can have your own characters for your profession needs, or just love leveling alts, this is an in-depth (lots of info) guide for the fastest leveling experience and can point you in what to do to make heirloom collecting less of a pain up to your commitment level. Introduction: Updated to 6.2.3! Updating as we get more data.