You see triangular carpenter's squares in every home center because the design has some unique advantages over a conventional square. This scaled-up, super accurate Woodpeckers version brings those advantages from the jobsite to the woodshop.
The 12" length won't fit in your apron pocket, but that's kind of the point: a larger square's longer legs have more reference length than a small square. The entire body is machined from 1/4"-thick aluminum for outstanding accuracy and stiffness, and the holes in the body make it easy to handle and hard to drop.
The broad triangular shape balances comfortably and is inherently more stable than a square when laid across a board. There's also the 45-degree edge not available with conventional squares for precisely setting blade tilt on table saws, setting table tilt on larger band saws, and all sorts of other alignment and inspection jobs around the shop.
The full-length base provides a lot of reference area for positioning the square accurately along the edge of a board, and it allows the triangle to stand upright. The base can also be quickly removed for times when the entire square needs to lie flat, such as when you're setting up table saw jigs
