Greenroom136 Rainmaker vs. REI Co-op Flash Pack 22

The Greenroom136 Rainmaker by Greenroom136 is indeed a solid pack, engineered with functionality as its focal point. With specifications of 40 inches by 28 inches by 21 inches, the Rainmaker is a robust and spacious backpack offering 22 liters of capacity. It sports a distinctively rugged exterior made of 1000D Cordura, enhancing its durability and longevity, a nifty laptop compartment that can comfortably accommodate a 15-inch laptop, and receives admiring nods from airline cabins across the board, due to its 100% compatibility rate. It weighs around 1.7 pounds, providing a sturdy yet comfortable carriage experience. As one reviewer aptly noted, it's a "complete package at an amazing price for anyone looking for a handmade EDC pack."

Turning our attention to the REI Co-op Flash Pack 22, the first attribute that strikes you is its minimalistic yet smart design, focused only on necessary features. It shares the same capacity as the Rainmaker (22 liters), with a slightly taller structure (46 inches) but a lesser width (26 inches); both backpacks having the same depth (21 inches). The Flash Pack 22 is made of nylon and comes with a laptop compartment suitable for a 15-inch laptop just like the Rainmaker. However, the most impressive aspect is its weight - a mere 0.4 pounds. Indeed, as one reviewer commented, it's the best budget daypack of the season.

Here are the comparison bullet points:

• The Greenroom136 Rainmaker and the REI Co-op Flash Pack 22 are both compatible with all airlines and have identical capacities (22 liters).
• The Greenroom136 Rainmaker has an edge regarding customizability options and its water-resistant exterior, while the REI Co-op Flash Pack 22 prides itself on its utilitarian, minimalistic design.
• The Rainmaker, being 1.7 pounds, is heftier than the Flash Pack 22, which flaunts being featherweight at a mere 0.4 pounds.

The Greenroom136 Rainmaker offers sturdy and versatile carry-on solution, with a bevy of customization options, highly organized compartments and assuring water resistance. On the other hand, the REI Co-op Flash Pack 22 emerges as an extremely lightweight, bare-bones design that's exceptionally comfortable with a great suspension system, even when full. Purchasing either of these would primarily come down to your specific needs, whether it’s for an adaptable, everyday carry or an ultra-light trek companion. Both bags stand out in their respective domains, offering the collective promise of quality, function, and durability.