The Loyalty Gun cannot capture airborne units or enemy ACUs. It may capture anything else: land units, naval units (including submerged units), and structures.
The Loyalty Gun has an impressive range of 175 units (for reference: point defense is 40/45 units) and thus needs radar to use effectively.
The Loyalty Gun capture time for common units is 2 seconds, minor experimentals 5 seconds, and major experimentals 10 seconds. Shields and armor have no bearing on the capture time.
The only way to prevent a unit targeted by the Loyalty Gun, from being captured, is to move it out of range or destroy the gun.
Loyalty Guns are a great way of punishing "turtlers" or someone using massive amounts of small units like Titan Assault Bots as 3 to 4 Loyalty Guns can easily handle small units and capture multiple experimentals.
It's most effective at capturing experimentals as it is the only unit which can capture them with any speed. From there, the experimentals can wreck the remainder of forces attacking you and even be turned back on your attacker.
The Loyalty Gun can be used to take down a well defended enemy stronghold due to its range and ability to capture structures, especially when self-destructing enemy buildings that have been captured which are no use to you.
The Loyalty Gun ignores shields. Steal your enemy's shield generators - mobile or static - and cause them to wander off or self-destruct, or simply watch your enemy's units kill them for you.
Capturing enemy buildings or units in defensive positions can tempt their own point defenses to shoot at the new targets, which allows the Loyalty Gun to both rapidly debilitate bases and distract enemy firepower. Likewise, it can slow or distract incoming enemy forces by converting them one at a time.
This weapon is one of the few ways the illuminate have of dealing with being bombarded by enemy naval units.
Keep in mind that the Loyalty Gun is inefficient in defending against large groups of units.
The Loyalty Gun is best used as a siege weapon, efficient against "turtlers".
Multiple Loyalty Guns can not target the same unit, but they can decimate an incoming force. However, it is a common pitfall to rely too heavily on Loyalty Guns - point defense and shields are still necessary to handle any remaining forces.
There appears to be a bug where training upgrades are reapplied to units captured by the Loyalty Gun (HP increases after capture).
Maps like the Geothermal borehole is a good place for the Loyalty Gun as its range can just about reach into the enemy base if you take control from the center. if not then you can capture any mass extractors on the side overhang of each bridge that isn't allied.
Capturing Engineers allows you to build your opponent's structures. The Loyalty Gun is very, very good at doing this as it will seek out units in a huge radius. Engineers sent to build structures in remote points are often stolen by the Loyalty Gun, as are those sent to attempt to recapture the area. You can then use this to (for example) supplement an Illuminate force with long-ranged Mastodon cruisers, or build clumps of point defenses in or near the enemy's base.
Don't expect captured units (or buildings) in the middle of an enemy base or attack force to be of any use to you. They will be destroyed rapidly. The main use of this is in chipping away at enemy bases from a safe distance, with much greater accuracy and reliability than artillery, or distracting enemy units in order to cause them to fire at their erstwhile comrades momentarily. Capturing Experimentals from oncoming armies is a highly viable tactic however; it not only removes a priority target, but forces your enemy to deal with a large threat that's suddenly appeared in the heart of his force.
If you plan on launching a major land (or sea) attack against someone and suspect them of having Loyalty Guns, take out the guns first. Precise attacks such as Noah Unit Cannon deployments, jump jets and teleportation can allow you to drop a small force of land units near the structures and destroy them rapidly. Artillery (or your own Loyalty Guns, if you're lucky!) can slowly wear them down or steal them before you move into engagement range of your enemy. Alternately, make a mass rush of cheap land units first, dealing damage and destroying the defenses, before sending in your experimentals. Use Jump Jets to close in since this makes your units temporarily immune to the Loyalty gun.
Building multiple Loyalty Guns can have a major impact in land and sea force engagements as they can allow your smaller force the advantage of extra units that will draw the attention of the other units. also multiple Loyalty Guns can allow you to easily decimate an enemy force and possibly give you back a small portion of that force to send back.