The Fitbit Flex 2 is the successor to the original Flex, which was launched three years ago and considered by many as Fitbit's most iconic product.

Like the original, the Flex 2 is a simple fitness tracker with no LCD screen, GPS function and heart- rate monitor. It has only five LED lights to show the progress of your daily step goal.

But it is Fitbit's first waterproof fitness tracker with a 50m water-resistance rating. Thus, it can track your swims, even in open sea, in addition to the usual steps, runs and sleep monitoring.

Flex 2 consists of a tracking module and a rubber wristband. Out of the box, you get two different-sized - small and large - wristbands.

Charge the module and insert it into the wristband to start tracking your daily activities.

Many fitness trackers, such as Fitbit Charge 2, have LCD screens that make them bulky and heavy. But at around 30 per cent smaller than the original, the Flex 2 is so small, light and comfortable that I do not even feel I am wearing it at all.

And to make the Flex 2 even more enticing, Fitbit is selling a range of bangles (in silver, gold and rose gold - from $139.95) and pendants (gold and silver - from $129.95) that you can insert the Flex 2 tracker module into.

I tried the silver bangle and found it comfortable and sleek. With these accessories, the Flex 2 easily doubles as a fashion item.

In terms of steps tracking, the Flex 2 delivered almost identical readings as my calibrated Charge 2. And it is smart enough not to count arm swings as steps taken, when you are not actually moving. However, it does not record stair-climbing stats.

The sleep-tracking function is also very accurate. It correctly tracked the time I fell asleep and the time I woke up. Toilet breaks in the middle of the night are included in the awake time.

Without a heart-rate monitor and GPS function, running metrics are limited to calories burnt and steps taken.

For swim tracking, the Flex 2 can track only the number of laps (you have to enter the lap length in the Fitbit app) and calories burnt. It does not record information about your swim strokes and lap times. The few times that I swam with it, I found the lap counting a lap short.

Battery life is average for a fitness tracker, at around four days with each full charge.

• Verdict: If all you want is a lightweight, comfortable and basic fitness tracker that you can swim with, the Fitbit Flex 2 is the one to get.