The Apple Watch Series 6 looks like its predecessor, the Series 5, which also looks like the Series 4. You get the same rectangular watch case with a crown and button on the right side.

While this might disappoint some, it does mean all the watch bands that current Apple Watch users have are compatible with the new smartwatch.

The Series 6 comes in four new case colours: blue and red aluminium, as well as stainless steel in graphite and gold.

The Straits Times reviewed the graphite stainless steel model, which comes in a lighter shade of black compared with the space-black stainless steel of previous models. This subtle change makes the watch look even more sleek and exquisite.

The Series 6's always-on display is 21/2 times brighter than that of the Series 5, according to Apple. It does look brighter to me and I find it much easier to read the time and notifications on this display under bright sunlight.

Inside, the Series 6 has several upgrades - including the new S6 chip, which offers faster performance than Series 5's S5 chip.

The Series 6's always-on altimeter, a new feature, is able to measure elevation change in real time. It was fun watching the readings going up as I rode the lift to my flat.

But, while it is mostly accurate, there are fluctuations at times. For example, one reading is 60m when I am at home, but at other times, it measures 30m or 40m.

The Series 6 is able to measure oxygen saturation, also known as SpO2, with the new blood oxygen sensor and app. It will continue measuring even when you are asleep.

This is in addition to the same health and fitness features - such as heart-rate monitoring and electrocardiogram (ECG) screening - that can already be found in the Series 4 and 5. And with Apple's new watchOS 7, the Series 6 can track your sleep as well.

While the new watchOS is supported on models as old as the Series 3, the faster S6 chip makes everything in the Series 6 more responsive and intuitive.

Other new features include a hand-washing reminder. The built-in sensors will automatically detect when you start washing your hands. A timer will appear, counting down from 20 seconds - the recommended duration of hand-washing - which is a handy feature to have in this pandemic.

Plus, you can set reminders to wash your hands when you reach home by using geo-location with the built-in GPS.

But, due to GPS triangulation limits, the reminder does not work if you are not far enough from home.

For instance, after getting lunch at a coffee shop a block away, the watch does not remind me to wash my hands. But it sends me a reminder after my grocery run at a supermarket farther away.

The watchOS 7 offers several new options for watch faces, such as Chronograph Pro and Typograph. But my favourite is the GMT face, where the digital bezel comes in Pepsi blue and red - the same colours of my dream timepiece, the Rolex GMT Master II.

With the GMT face, you can select the second world-time by rotating the crown to find the city you want. And the second hour hand will point to the bezel to show the selected time. This is great for video-conferencing meetings with people in other countries - and, potentially, for travelling in the post-pandemic future.

In terms of fitness tracking, the Series 6 is as good as it gets. For step tracking, the readings are very close to those of my own calibrated Series 4, with a mere difference of 50 steps.

On my usual 5km jogging route, the GPS-tracked runs by the Series 6 are only around 10m to 20m off.

However, the watch's sleep tracking can be better. It does not automatically track sleep, like what Fitbit and Garmin's fitness trackers and smartwatches do. You have to set the time you sleep and wake, or manually turn the sleep mode on and off.

Plus, it only shows your sleeping hours. There is no breakdown of light and deep sleep, which is not very insightful.

Battery life is slightly better than that of the Series 5. When I have the watch paired to an iPhone with notifications turned on and a 5km run recorded, the battery has around 50 per cent power remaining by bedtime, compared with 40 per cent in the Series 5.

The Series 6 also offers faster charging, juicing up from zero to 80 per cent in an hour. I also found that only 6 per cent of its battery life was depleted after six hours of sleep.

For those using the Series 5, the Series 6 is not much of an upgrade. For users of the older models, like myself, it is probably time to upgrade to the Series 6.

However, if the price - which starts at $599 - is a concern, Apple has introduced the more wallet-friendly Apple Watch SE, which is priced at $419 and up. It looks like the Series 6, and has the same S5 chip as the Series 5 and an always-on altimeter like the Series 6.

It lacks the SpO2 and ECG features of the Series 6, but if you just need basic smartwatch and fitness functions, the SE should do the job.