Please note the links below are currently to 6.x class guides. Updated guides are in progress.
Combat Style Legendary Implants
Legendary Implants can be purchased and upgraded on the fleet in the Supplies section. A player can equip two implants and so can equip up to two Legendary Implant bonuses.
Squad Lead Package
Whenever you take damage with Energy Shield, a weaker shield is applied to nearby allies for 3 seconds. Package contains Absorption Rating.
Comments: This buff is fine but a group mitigation buff is not that strong or useful for a non-tank discipline. Not recommended for Mercenaries.
Advanced Scanning Package
Reduces the cooldown of Healing Scan by 1.5 seconds and the cooldown of Emergency Scan by 3 seconds. Package contains Alacrity Rating.
Comments: Advanced Scanning sounds interesting for healers but needs context to evaluate its usefulness. Healing Scan has a 12 second cooldown and Emergency Scan has a 21 second cooldown, so their cooldowns are reduced by 1/8th and 1/7th, respectively. Healing Scan and Emergency Scan are strong heals so more uptime is nice. However, Healing Scan usage depends more on uptime of Supercharged Gas to temporarily remove its cooldown and far fewer uses come outside Supercharged Gas windows so the uptime benefit is smaller than one might initially think. Emergency Scan will generally be used on cooldown so more uptime is great though due to its longer cooldown the positive impact on healing is somewhat limited.
So that leaves Advanced Scanning decent but not amazing. What about the competition for healers? Concentrated Fire is an alternative that gives an auto-crit heal (or attack) every Supercharged Gas and Random Charge will give several extra uses of Supercharged Gas per encounter. None of these are clearly better than the others on first glance. All three buff sustained healing. Advanced Scanning and Random Charge make energy management slightly easier in different ways. Concentrated Fire is probably less powerful for sustained healing but having control over your buff to improve burst healing to triage players is more useful healing than a sustained buff over the course of a fight.
I can not make a conclusive recommendation so would suggest choosing between these three implants based on your personal playstyle and what feels most comfortable. Another consideration is that Concentrated Fire and Random Charge are highly likely to be optimal for damage disciplines, so running those two might enable Mercenary players to only need two legendary implants for all three disciplines. My personal playstyle favors Advanced Scanning and Concentrated Fire for healers since it avoids the RNG of Random Charge.
Concentrated Fire Package
Activating Supercharged Gas makes your next Rail Shot, Mag Shot, or Emergency Scan critically hit or heal. Package contains Critical Rating.
Comments: Concentrated Fire provides the weaker bonus from the 6.0 Concentrated Fire set bonus. The buff is nice but not massively powerful to provide an extra auto-crit every Supercharged Gas window. I recommend this one along with Random Charge for DPS primarily because there are no other good damage options. Target Eliminator's buff is too weak and does not have full uptime and both Advanced Scanning and Squad Leader do not buff damage. Concentrated Fire is a solid option for healers as well though its debatable which to take among it, Advanced Scanning and Random Charge.
Random Charge Package
Damaging an enemy or healing an ally has a 10% chance to generate a stack of Supercharge. Cannot occur more than once every 5 seconds. Package contains Alacrity Rating.
Comments: I greatly dislike the RNG of Random Charge but extra Supercharged Gas windows are very powerful for all Mercenary disciplines and particularly for Innovative Ordnance where Supercharged Gas deals a lot of extra damage. I recommend Random Charge for damage disciplines and it is one of three options for healers along with Advanced Scanning and Concentrated Fire.
Target Eliminator Package
Heatseeker Missiles and Serrated Shot increase damage dealt by 2% for 15 seconds. Cannot occur more than once every 30 seconds. Package contains Critical Rating.
Comments: I really like the idea of Target Eliminator to add a flat and consistent damage buff. I really dislike the 50% uptime and the weak buff. I hope this legendary is adjusted to remove the "cannot occur more than once every 30 seconds" to allow full uptime. For now I would not recommend Target Eliminator for any disciplines.
Combat Style Tacticals
Unless otherwise noted, all tacticals can be purchased on the fleet in the Supplies area for 3,000 Tech Fragments and 1,000,000 credits. They may also be available from Kai Zykken in his rotating inventory for 2,000 Tech Fragments and 1,000,000 credits.
Cool Your Jets
Rocket Out vents 20 Heat and immobilizes enemies around you for 2 seconds as you leave.
Comments: A neat PVP utility for heat management and immobilizing melee DPS while kiting. Not useful in most situations though.
Jet Boost increases your movement speed by 50% for 3 seconds. For each enemy hit with Jet Boost, the cooldown of Hydraulic Overrides is reduced by 3 seconds.
Comments: Not a great tactical. I find that Hydraulic Overrides and Rocket Out together are plenty of utility for movement speed, so I want DPS/HPS boosts from tactical items for Mercenary disciplines.
When you use an ability with Power Surge, that ability is not put on cooldown.
Comments: This utility sounds interesting to enable a double cast of a strong cast ability via Power Surge. The tricky part to this tactical is that apart from fillers most really powerful discipline abilities are either instant or channelled, greatly limiting its potential utility.