The Fitbit FB403BK-WMT Flex 2 is a sleek, waterproof activity tracker that has garnered a mix of praise and critique from its users. Its compact size and waterproof feature make it a favorite for those who prefer a minimalist design and need a device that can withstand water exposure, including swimming.

Users appreciate the device's ability to send text and call alerts, which helps reduce the need to constantly check their phones. The silent alarms are also a hit among heavy sleepers, effectively waking them without disturbing others.

However, some users have reported issues with the step counter accuracy, noting that it sometimes counts arm movements as steps. The sleep tracking functionality is less detailed compared to other models like the Alta HR, which might be a drawback for those who prioritize detailed sleep analysis.

Durability is another strong point, with several users reporting years of daily use without significant issues. The option to switch bands allows for personalization and style changes easily.

On the downside, there have been complaints about defective units that cannot be charged and difficulties with the return process. Additionally, some users miss features like stair tracking and more comprehensive sleep tracking.

Overall, the Fitbit Flex 2 is ideal for those seeking a basic, durable fitness tracker with essential features in a small form factor. However, potential buyers should be aware of its limitations and occasional quality control issues.