Everything old is new again. Remember the old Nokia or Motorola slider phones? Well, such phones are back, sort of, with Oppo and Xiaomi re-imagining the slider design to achieve an all-screen smartphone.

Last year's Oppo Find X uses a motor to move its pop-up camera, but Xiaomi's flagship Mi Mix 3, launched here earlier this month, requires you to slide the screen downwards - to reveal missing headphone jack and the the front camera underneath - by hand.

The slider mechanism clicks satisfyingly into place, aided by magnets. For added dramatic effect, the edges of the screen light up when you slide the screen down.

Xiaomi has even created five sound effects for the sliding motion - my favourite is the Warrior, the swish of a sword when unsheathed that you hear in movies.

The Mi Mix 3's human-powered way is arguably better as there is no risk of the motor breaking down. It is easy enough that a child can do it. But when I hold it up to the light, there is just the tiniest gap between the two layers of the phone, which leaves a tiny doubt on the long-term durability of this design.

Yet, the sliding action is very addictive, like clicking a pen or fiddling with a fidget spinner. I found myself playing with the phone most often in the lift, idle and bored without an Internet connection.

Xiaomi says the sliding mechanism is tested to last 300,000 cycles. In addition, you can customise the phone's behaviour when you push down the screen, from opening the camera app for a selfie to opening a specific app.

Because of this slider design, the Mi Mix 3's 6.4-inch display does not have a notch - except for a thin chin, it is virtually all screen. It is a 1,080p Samsung-made Oled screen that looks great with punchy colours and is bright and usable in the sun.

But the slider design makes it practically impossible to waterproof the phone and also increases the thickness and heft. Xiaomi is not doing its phone any favours by using a ceramic back, which feels premium, but is also heavier than the usual glass back. The Mi Mix 3 weighs 218g, which is more than the weight of the Samsung Galaxy Note9 (201g).

A minor issue - you may have trouble finding a case for the Mix 3 because of its slider design. The good news is that Xiaomi includes one in the box. This plastic case has a nice, soft-touch finish, though this layer started to peel off after just a week. Another useful extra in the box is a fast wireless charger to complement the wireless charging feature in the Mi Mix 3.

Enthusiasts may bemoan the lack of a microSD card slot. The bottom-firing speaker, while producing a decent volume, was easily muffled by my hand while using the phone in landscape orientation.

Like Samsung's current flagship phones, the Mi Mix 3 has a dedicated button that triggers a virtual assistant. But while Samsung uses its own Bixby assistant, Xiaomi has chosen the Google Assistant which, in my opinion, is more useful.

It has the hardware of a flagship smartphone, like a high-end Qualcomm Snapdragon 845 chip and 6GB of RAM - there is a variant with 10GB RAM. But the feature that makes it a top smartphone is its dual rear camera system.

These cameras - both 12-megapixel units with one being a telephoto camera - are excellent. They offer optical image stabilisation and 2x optical zoom. There is very little shutter lag and the autofocus is fast.

There is even a handheld night photography mode that requires you to hold the phone steady for a couple of seconds (long exposure shot) for better low-light photos.

Photos turned out crisp with little noise. Colours look vibrant and accurate. The night shots were impressive, with the handheld night photography mode capturing details while keeping noise at an acceptable level. Highlights from light sources were well-done and not overblown. While it is not as amazing as the Google Pixel 3's Night Sight mode, the Mi Mix 3 is definitely one of the better smartphones for night photography.

It runs Xiaomi's MIUI 10 interface, based on Android 9. There is no app drawer to display installed apps and Xiaomi, like most manufacturers, have preloaded its own set of system apps, including a browser, calendar and clock.

But I found its full-screen gestures, which lets you navigate the interface without the usual Android soft keys, intuitive and user-friendly. These gestures make full use of the phone's near-bezel-less screen.

Least impressive is its battery life. Its 3,200mAh battery is modest for its 6.4-inch screen, so you likely need to charge it every day. In the video-loop battery test, it lasted 11 hours and 10minutes - decent but not fantastic.

•Verdict: The Mi Mix 3 is a unique slider smartphone that offers flagship-tier photography capabilities without breaking the bank. But it is heavy, possibly fragile and has average battery stamina.