The AR compensator is described as:
Reduces recoil. It is incompatible with suppressors.
It can be found in northern Itacua, in Buena Vida Town. The accessory case is upstairs in a building at the back of the town. The “Amaru’s Rescue” mission is nearby.
Although the cartel presence here is reasonably high, this is Itacua afterall, the easiest province. If you want to avoid conflict you can circumvent the bad guys by going around the edge of the town, or approach from the west by helicopter as I did. You can then easily take down anybody in your way and walk into the building.
The compensator muzzle reduces recoil which is great and this is so easy to collect you may want to try it. Although you may prefer to grab the Compensator V2 for assault rifles available in Monte Puncu which reduces recoil further.
However it slightly reduces noise reduction, and the big caveat with all compensators for all guns is that when used, you can no longer equip the suppressor on your gun. For me, that’s a deal breaker, so I personally never use the compensators, but have a try and let me know in the comments how you find it.