The AKS-74U was originally designed for use by vehicle crews to allow them to easily maneuver during combat.  The 8 inch barrel makes the rifle idea for tank crews and is also used by the police as close combat weapon.  While the AKS-74U provides more power than a pistol caliber sub-machinegun, its drawback is the increased recoil and muzzle climb.  The weapon also tends to be inaccurate at long ranges due to it's barrel length.  The AKS-74U has been fitted with numerous add-ons to make the weapon more versatile in the field.  The most notorious of these add-ons is the grenade launcher which is mounted under the lower hand guard.  This feature allows the weapon to be used against larger, more heavily armored targets.   However the grenade launcher substantially increases the weight of the gun, decreasing in mobility. 

There are two other variants of AKS-74U one is chambered in 7.62x39(AKS-74S) and the other is in 5.56 NATO.  Both are nearly identical to the 5.45x39 version.  The 7.62x39 version uses both drum magazines and stick magazines. The 5.56 and 5.45x39 versions only accept stick magazines and have far less recoil than the 7.62x39 version.     

U.S. Versions:

Very few AKS-74U's if any were imported into the U.S., the ones that did make it are registered as machineguns.  You can expect to pay $10,000 and up for an authentic AKS-74U. A semi-auto version can be built from a krinkov parts kit on a pre-ban receiver.  However in order to do this you must register the weapon with the BATFE as a Short Barreled Rifle.  You can also assemble a Krink kit on a registered machinegun receiver and have the real thing.  You can not assemble this kit on a post-ban receiver (unless you are law enforcement) due to U.S. law, and the ability of the weapon to function correctly.