In terms of general performance the P831 is mostly very slow. It starts up quickly enough, in well under two seconds, and also shuts down nice and quickly. In single shot mode the shot-to-shot time seems to vary wildly depending on the camera settings and the light level, but can take as long as six seconds, with a "Busy…please wait" message on the monitor. In other conditions it is quicker, but even at its fastest it still takes around three seconds per shot. In the continuous shooting Burst mode it still takes about 2.7 seconds per shot, which lends a whole new definition to the word "burst". At least it has an audio cue and monitor view while shooting.
The P831's biggest weakness is its autofocus system, which is simply terrible. It's the only camera I've ever found that wouldn't focus on my cathedral window test shot, in other words it wouldn't focus on a large, well-lit subject with plenty of detail and contrast. Needless to say its low light performance is pretty much entirely absent, and even when it can focus on something it takes a long time and often several tries to get it right. Obviously it has no AF assist lamp, and its low-light performance is further hindered by the underpowered flash.
Overall image quality is also pretty ropey. Even in its highest quality setting it uses a particularly fierce compression algorithm, resulting in picture files that average around 2MB, very small for an 8MP camera. Pictures lack colour, detail, tone and dynamic range, and the lens also produces significant barrel distortion and chromatic aberration. Noise control is also very heavy handed, with shots at 200 ISO showing blurring from noise reduction. Many wide-angle images also showed heavy vignetting, with murky dark shadows in the corners of the frame.
As well as these problems the P831 also seems to have a big appetite for batteries, eating a set of new Duracell Ultra AAs in less than 100 shots.
The Genius G-Shot P831 is a very cheap camera, and ultimately you get what you pay for. While in good light with nearby subjects it can turn in a reasonable average snapshot, its slow performance, extremely poor autofocus system, low quality optics, underpowered flash and heavy handed compression and noise reduction mean that good quality photos are beyond its capabilities. If you are aware of these limitations and still want a camera for under £70, go ahead and buy it.