Build quality & functionality
To keep costs down, the Yongnuo is constructed from plastic but seems well made, although I'm not sure it would take being knocked over accidentally.
The black panel at the inner lower area of the ring houses all the controls. Along the top is the main on/off switch and a knob that is rotated to adjust brightness. A tripod bush and two coldshoes (a third is located at the top of the ring) allows for the attachment of a mobile, camera or a microphone.
The rear houses slots for two batteries, the mains socket and two USB ports that can be used to recharge smartphones and similar devices. Also located on the back is a small display with three function buttons beneath. The channel (Ch) button offers eight settings for use with the supplied bluetooth remote. The Battery (Bat) button allows you to get an idea of how much charge remains, while the Coarse/Fine button alters the brightness levels in 1% or 10% jumps depending on whether you prefer precision or speed.
On the front of the panel is another display so that you can check settings from the front, ideal if you're a vlogger shooting your own videos. Set 1 and Set 2 buttons allow you to lock brightness levels, while Whitening adjusts the brightness. The Mode button allows you to illuminate sections of the ring, choosing between the left, right, upper or lower half, or lighting the upper left and lower right, or upper right and lower left areas of the ring. Further controls are found on the remote, allowing you to adjust the brightness of the 3200K and 5500K LED lamps independently. A Yongnuo app with similar controls is also available for use.

Ease of use
The ringlight is attached to a lighting stand via a platform that offers a tilt facility so it can be angled up or downwards. It's easy to adjust the angle via the large knob, but I am concerned it might wear/break with use as the plastic fixings don't seem too robust.
The YN808 is straightforward to use as there aren't too many controls and buttons to work out. The instructions explain features but the translation to English does leave you deciphering the meaning in places – the purpose of the Whitening mode in particular is unclear, while the Yongnuo iOS app, while usable, could be improved.

Performance
There were no issues with the YN808's performance. I set up the camera's White Balance using a grey card at the start and found the colour temperature fairly consistent at different brightness levels.
A quick depression of the brightness button lets you either allow the 3200K LEDs to come into play when the 5500K LEDs reach maximum brightness, or keep them off. I found I used the remote more than the unit's controls as it is simple to set up and use.
The bright 5500K LEDs are ideal when you want a clean light output, but I found experimenting with the 3200K LEDs and the camera's WB settings produced good effects too. Moving the subject towards or away from the YN808, as well as adjusting its brightness, allows you to mix its effect with ambient light for creative results.
At around £200 (the price does fluctuate a fair amount), the Yongnuo compares well against many of its rivals. Brands like Nanguang offer similarly-priced models that while not as large or offering the same range of features, are available through traditional UK outlets. Models from other budget brands like Neewer (sold through Amazon) are closer in specification and price to the Yongnuo, but aren't as large.
Verdict
There are several decent portrait ringlights available from the likes of Nanguang and Rotolight, but this Yongnuo has the advantages of a large diameter, good range of features and an affordable price. A fine choice for portraits, still-lifes or video.