Once you unlock HK-51 the unlocks under the Legacy Perks Tabs appear on each of your characters. There are two there, one for each side. And you will be able to select the correct faction unlock at that point.
I got HK on my lvl 50 Vanguard, then unlocked him via the legacy perk on my lvl 3 Bounty Hunter. He had all lvl 50 gear on him, which was flagged as inappropriate or whatever. The stats on the companion tab for him reflected base level one stats, so none of the gear was giving him any stats at all. He still perfromed though and did a little damag. I didn't know his 'scaling gear' was bugged so I took it out. Now I will just put new appropriate gear in there. Good think I have a cybertech.
Oh, and Justin, I use shift+E for my boost too.