The MAC-10 is a .45 caliber Machine Pistol which fires round at a high rate, it has a short range and heavy recoil. It delivers very high damage(highest damage and the highest rate of fire.)
The rate of fire is 1145 RPM which can be compared with the K10. The Battlefield Hardline MAC-10 Machine Pistol can be used with both the factions.
The most easiest way to unlock the Battlefield Hardline MAC-10 Machine Pistol is by completing the Professional Assignment. It is easier said than done as you need to do a host of things for completing the Professional Assignment.
The disadvantages of this pistol includes very heavy recoil and a small damage drop-off while shooting from a long range. Also the MAC-10 Machine Pistol has the lowest magazine size in its class. You can nullify this by adding extended magazines to the Pistol. Since this is a short range pistol, it is highly uneffective against longer range targets.
For completing the first Professional Assignment a player needs 2 Bronze service stars, 10 Sniper Rifle kills and 5 Laser Tripmine kills. In the second Professional Assignment you should get 7 bronze service stars, 25 Sniper Rifle kills and 5 camera coins.
Getting the camera coins is also a task in itself, you will need to have 10 enemies spotted by your camera when you are killing them, for getting one camrea coin. An easy way to get camera coins is using a TDM server with 64 players and placing your cameras at proper locations from where they can capture your killings.