The drone has a Combi Rifle, Forward Observer, Flash Pulse and Electric Pulse as weapons. Because it has a Sensor it can perform Triangulated Fire and shoot at a -3 penalty ignoring all other modifiers as a long skill. It can also perform Sat-Lock to target an enemy in it's ZoC or the ZoC of any Sniffer.
In melee it's poor CC stat means it will almost always be better to use Electric Pulse and hope for a poor roll from the opponent (a 35% chance) than to try and fight it out.
Drones are almost always better shooting than Dodging, if they have the option, because of the usual -3 penalty on Dodges and Change Facings that REM troopers suffer. A drone's Silhouette is vertically smaller than a standard trooper making it easier for them to take some kinds of cover, which they will need as they cannot go prone.
Because it has Structure instead of Wounds this unit possesses a second Unconscious state. In effect, it takes one more wound than normal to remove them from the table. It also ignores the "straight to dead" effect of Viral and Shock ammunition.
G: Remote Presence grants Courage meaning it can always choose to not take a Guts roll.
M-Drones have a lot of utility. They can be used to expand the reach of a hacker allowing them to hack through its Repeater and gain a fire-wall bonus against enemy responses. Spending a few orders (ideally as part of a coordinated order) to move the drone up field and out of sight can allow a hacker to slow the advance of enemy HI, REM, TAG, and Hacker units.
Sensor on an FO platform allows for a few special tricks. Firstly you can use Forward Observation with the Triangulated Fire Long Skill provided by a Sensor and Target enemies far across the table. You can also make use of the special Sat-Lock skill to perform a Coms attack on an enemy in your ZoC of the ZoC of a friendly sniffer. This is a WIP -6 and if successful it Targets the enemy model. With an EVO this gets even better ignoring the -6 modifier.
Triangulated Fire "Ignores all other modifiers" meaning that if used on a trooper engaged in CC it will ignore the -6 to hit modifier. This means that missing you shot will never strike a friendly trooper but that the enemy will also not receive an ARO if outside of 8".
The M-Drone can place a Sniffer as a short skill or ARO allowing other models with Sensor to perform Sensor Sweep in within the ZoC of the Sniffer. Sniffer's also prevent enemies from Re-entering the camouflage state so it can help to limit enemy options. Sniffers also increase your are of Sat Lock.
With a Supportware program such as Overclock, the M-Drone's flash pulse can become a pain for the enemy, stunning their troopers and preventing Rambos from running your board, but it is best not to rely on this tactic and provide too many easy kills for your opponent.
Always remember that you can Engage with a drone and do not suffer a -3 on the PH roll to do so. This will usually doom the drone, but it forces an enemy to spend orders to get out of CC with them which can let your other troops Dodge out of LoF, deploy mines, or even fire into the melee and possibly kill the enemy.
M-Drones are easily killed by most attackers and since they represent both orders and tactical utility for your opponent it is always worth doing so. Keep in mind that their Flash Pulse is at a high effective BS (13 with a long +3 range band) and it is advisable to avoid taking multiple shots in ARO when you can. Also remember that it takes one more wound than normal to completely kill a trooper with Structure, so engineers may come an undo your work unless you confirm the kill.
M-Drones do well in most lists even without a hacker or sensor. They provide reasonably priced specialist and tools almost any force appreciates. In particular they are helpful as a backup MSV model (because of Triangulated Fire) and against enemy camouflage (because of Sensor Sweep and the +6 to discover rolls provided by this equipment. For most lists, it is good to consider a 25 package of a R-Drone and a M-Drone to make the best use of the M's Sensor and Sat-Lock skills.
Unless you have first turn and the enemy has already deployed a target that you want to Triangulate Fire on, don't put them in harms way. A M-drone brings equipment that empowers your force, and should be protected just like you would a Doctor or Hacker.
Active Turn Role
The M-drone has many active turn roles. It can move up the table and capture objectives as a specialist. It can hunt camouflage with its Sensor skill providing a +6 to discover rolls. It can set up for Guided Fire. It can clear enemy models out of CC with Triangulated Fire. It also has a Deactivator allowing it to Discover + Deactivate mines.
Generally it wants to avoid heavy firefights as it is has the same stats as a line trooper. Thus the M-drone is focused on the strategic side of the game rather than the tactical.
In almost all cases it will be better for the M-drone to respond with Flash Pulse instead of Combi Rifle because it has better range bands and higher WIP than BS. A M-drone is a good candidate for a Coordinated Suppression Fire order. It can benefit from support ware such as Overclock to increase its ARO.