I have found a couple of guides that are useful for your HK farming:
HK-51 | Companions details for all classes
SWTOR HK-51 quest guide -patch 1.5
We can use this thread for any tips, tricks or gotcha's with your HK-51 Companion.
Unlocking HK-51 on alts
Raising AffectionPer Count Sacula
Just a warning to those who unlock HK and plan on paying to unlock him for other toons. If the person who gets him is under level 50 all of his gear is unusable. I got him for my level 33 gunslinger and he has 5000ish health and no weapon. You can pull out the 50 mods and replace them with lower level stuff but I would imagine it could be a bit expensive.
Crafting BonusPer Zargs
And it seems the only way to get him to love you is to give him gifts. So far I used him on all dailys and not even 1 point.
+1 Mission Efficiency
+1 Crafting Critical
Gift Type Gift Affection Level Companion Statement Weapon favorite Conclusion: This should improve my efficiency. Military Gear like Courting indifferent Luxury indifferent Technology like Republic Memorabilia indifferent Imperial Memorabilia indifferent Cultural Artifact indifferent Trophy like Underworld Good indifferent
Assassinate: HK-51 takes careful aim at a target strong, standard, or weak enemy. Deals mortal damage. Requires and consumes 5 stacks of Target Eliminated. Only useable out of combat. Target Eliminated stacks are gained when HK-51 assists in defeating an enemy.
Blind Side: HK-51 takes advantage of a distracted target, firing a well placed decisive shot for extreme damage Can only be used on targets impaired by Evasion Protocols.
Evasion Protocols: Activates HK-51's Evasion Protocols, which drops a diversionalry grenade and causes him to leap towards you. The primary target is stunned for 2 seconds. Targets around HK-51 have 10% reduced accuracy for 4 secs.