For those of you who don't know, clipless pedals are a system that allows you to join a special cycling shoe to the pedal so that you can apply force to the pedal when pulling your foot up. They also attach your foot so that you press down with the ball of your foot, which will feel different if like me you cycle with "incorrect" method of using the middle of your foot on platforms (term for normal type of pedal). Despite the name 'clipless' you do actually clip the sole of your shoe into the pedal but they are called clipless as they differ from cycling straps that would enclose your shoe. The actual benefit of clipless pedals varies depending on the person and how you intend to use them. I am sure there are a large number of web pages debating this topic but the best way to make a decision is probably to try them yourself.
I use my bike mainly for cycling short journeys so I wanted a platform for using my normal shoes. I choose these over the variety that have the clipless SPD system surrounded by a platform as I wanted a good platform pedal in its own right rather than a compromise and was worried that the clipless socket would protrude and dig into the soles of my feet.
The first time using the platforms my feet instantly felt more secure on them than the black plastic ones that were included in my bike. Then the main drawback of using one sided pedals occurred as soon as I reached some traffic lights. While one foot would remain on one pedal ready to push down, by the time I has launched and put the other foot onto second pedal I would find it more often than not I was pressing down on the SPD and had to try and flick the pedal with my toes to get it to turn around. This was frustrating for a while but once you learn how to avoid this you can get the right side in seconds:
With my bike at least the key thing to notice was that the pedal will always tend to have the same side pointing towards or away from the centre of the cranks (where the pedals rotate around). So when I stopped at traffic lights with the platform side at the bottom of a rotation so pointing up and towards the centre of the cranks, by the time I had pushed down on the other pedal the platform side had rotated 180 degrees and now faced downwards towards the centre of the cranks. So if you shoe is on the wrong side of the pedal just push it down to the bottom and take your foot off and allow it to go back up on its own and by the top it should be the correct way up.
Sorry If that didn't make sense, two (fairground based!) analogies are that without being touched the pedal will behave like a cart going through loop on a rollercoaster always parallel to the track rather than a Ferris wheel where the carts are always the same way up. This is how it works on my bike but this could change if the joints were oiled differently, but either way it shouldn't be too hard to find a method that works for you.
Now I bought these pedals to use the clipless system for the occasional long ride. The pedals use the Shimano SPD system and you are able to adjust the pressure you need to apply to twist your foot in or out with a 3mm Allen key. I would recommend you start on the looser settings then get tighter as you become more confident. I use clipless in central London which is probably one or the worst places to use them with all the traffic lights, but if you really like the feeling of riding clipless this shouldn't be a problem, even here. I found the main advantage to clipless to be climbing shallow to medium gradients and better acceleration.
When buying these pedals you need to decide whether the inconvenience of only being to use one side at a time it still better than changing the pedals to pure clipless or platform each time. If you have never used clipless before then try to use them before buying all the clipless gear. Once you have decided you want half and half pedals these are the best you can get.