Oppo's R9s Plus and its younger sibling, the R9s, are a refresh of last year's mid-range R9 line, with a better battery, updated operating system and improved camera.

They retain the almost iPhone- look of the R9, down to the slight camera bump on the rear and the shiny gold ring around the fingerprint sensor. Both phones have 1080p Amoled screens, with the key difference being the size - the R9s has a 5.5-inch screen and the Plus has a 6-inch one.

I much prefer holding the smaller R9s, as it is the perfect size for gripping the phone solidly while still being able to use it with one hand.

The R9s Plus feels absolutely massive, but the sheer screen estate on it is a plus for multimedia junkies who can make use of it

The full-HD screens of both phones, along with the thin bezels at the sides, make them great to use and look at.

Their fingerprint sensors are still blazingly fast - one touch and they're unlocked, unlike older phones which take a noticeable millisecond to register and unlock.

Oppo prides itself on providing a great smartphone photography experience, but it feels like the Chinese manufacturer has hit a bit of an innovation slump with the R9s.

Don't get me wrong - the camera is still top-tier, standing out as one of the best among mid-range phones. Pictures are clear and sharp, because of the dual-phase detection autofocus technology and new sensors slapped onto the phones. The front-facing 16-megapixel camera also lives up to Oppo's selfie phone expertise. The front camera is sharp and bright, being able to take in more light due to its larger aperture which makes for some really clear self-portraits.

But the features which made Oppo popular in the first place - selfie mode, beautification features and filters and GIF animation - have been adopted by both rival companies or even apps that do the same thing.

Another thing Oppo got right with the R9s and Plus were their battery lives. They survive well into the evening with heavy social media use, texting, streaming videos and playing Pokemon Go, with just enough juice to make it in time to a charging point.

While the R9s is respectable on the hardware front, there is much to be desired in its software.

Oppo's ColorOS has not changed much from its previous build in the R9. While it is now running Android 6.0 instead of Android 5.0, it is still a dated piece of software as newer devices are now sporting Android 7.0.

Some of the design and user interface tweaks of ColorOS in the R9s line are a bit questionable. For example, swiping down on the notification bar displays the quick settings options first, and you have to swipe right to see your notifications.

This is particularly counter-intuitive, as the first thing I would want to see when I swipe down are my new notifications.

Another counter-intuitive feature is Oppo's placement of the soft navigational keys.

The back button is on the right of the home button, while the multi-window key is to the left.

Most Android phones have it the other way around. So it might take the seasoned Android user a while to get used to the Oppo.

Ultimately, the R9s line seems to be suffering from a bit of an identity crisis. They are high-end mid-tier phones, but may have been priced out of the competitive mid-range market.

Its price, especially that for the R9s Plus, comes very near to premium territory, which is inhabited by phones that have speedier processors , the latest software and better build quality.

•Verdict: Oppo's R9s phones occupy a strange niche, being mid-range phones which may be a bit pricey for most mid-range users. It shines on the photography and hardware fronts, but its user experience can do with more work.