The rai·son d'ê·tre. ABC/R's lower paddle is angled and protrudes further laterally, easily separating itself from the ambidextrous magazine catch's release paddle. It enables the user to identify and differentiate these two different components by feel, without a visual.
ABC/R's top paddle's upper half is angled at 10 degree, and lower half is angled at 5 degree, to make accessing the bolt release easier when the bolt carrier is locked back. Our good friend Nate Schultz (known on various social media as NSZ85) has influenced the ABC/R's top paddle design.
ABC/R has progressed to version 2 (v2), we continue to improve and refresh our products based on user input and real world experience. In v2, the lightening cuts have been removed, the upper paddle has been thinned down, and further tapered to accommodate thick upper receivers. The thinner upper paddle resulted in similar weight saving as afforded by the original v1's lightening cuts, while improving compatibility with non-TDP spec, thicker receivers.
The horizontal serrations of the top paddle continue further below, and terminate at the notch. The additional serrations here help provide more traction on the ABC/R's top paddle.
The notch immediately above the ABC/R's lower paddle serves an important function. It provides tactile feedback to the user as to the location of his finger on the bolt catch, and differentiates the two control surfaces on the ABC/R (upper paddle and lower paddle) without having to visually identify them. Visual identification takes time, and isn't always possible in low light conditions. This design input came from the famous gear guru, Military Morons.
Side by side with a factory bolt catch can easily illustrate the kind of difference a thoughtful design can bring to a human to machine interface. Every angle, increase or decrease in surface area and location of serrations has a practical reason. Little known fact: the 10 o'clock notch on the ABC/R's upper paddle isn't for looks. When the AR slides into a case, we don't want sharp corners to rub against the case to create drag and accelerate wear on the bolt catch's finish. The 4 o'clock notch was then created to give the upper paddle a symmetric look, probably the only nod to aesthetics on the entire design.