The standard A3 upper receiver is pretty good, and hard to improve on (cosmetics don't count), but there are couple of areas  people the manufacturer would change.  It was one of these "why can't they make it like this, it'd be easier/better" that led to the URF.

URF is based on CMT's URPR-1 7075 billet upper receiver.  Type 3 hard coated in black, it is an excellent basis for the two ergonomics driven changes that wanted.

Relief cuts on the section before rails start for better accessibility of a flip up BUIS's sight stalk / flip up element.

Relief on the top of forward assist housing.  The relief cut is specifically designed for ambi charging handle users. When the user uses his right fingers to pinch and grasp the CH's right latch, the relief allows the index finger to reach down further, so the CH's right latch is positioned in the middle of his finger pad, not the tip of it,  for a more secure purchase, especially if the user has gloves on. When user use left fingers to grab the charging handle's left latch, there is nothing below the latch, but on an upper with forward assist, its housing stands in the way. The relief simply provides what room that can be spared on the FA housing so more of the user's finger can have a positive purchase.

2020 production URF v2 has done away with the over pressure gas relief port.   It has retained the relief that clears the LMT MARS-L lower receiver's right side bolt catch, and thus compatible with MARS-L.

Features:

• 5 axis machined from 7075 T6 billet
• M4 feed ramps
• Engraved “T” numbers
• 1913 picatinny Rail flat top
• MARS-L compatibility
• Mil Spec Type III class II hard coat anodized Black
• Shell deflector
• Forward Assist machined into receiver (on standard URF v2 only, URF-S v2 has no provisions for a forward assist)
• Dust cover port machined into receiver
• Increased wall thickness for added rigidity
• Compatible with Mil spec parts
• Compatible with most aftermarket handguard/rail systems
• Lifetime warranty against manufacture defects
• Anti-rotation hole above gas tube hole
• Compatible with "Tactical Link" Enhanced Battery Assist Lever
• Compatible with LMT MARS-L lower receiver
• Comes stripped without dust cover & forward assist assembly
• Weight: 8.9oz (URF v2), 8.56oz (URF-S v2)

Please NOTE: Since 2022, begun to phase out feature #2. The relief cut is very shallow, and most users don't notice the difference between the FA housing with, and without the relief cut.  If you received a URF-B v2 without the relief cut on the FA housing, it's normal.  URF-B v3 will not have this feature.