We needed a guard to use at home when our 2 year old granddaughter stayed with us. We also wanted to take it away with us to our caravan. This was one of the few I could find in a neutral colour. I searched on line for information on how to fit it, but this was very scarce and too vague so ended up emailing Tippitoes who were very helpful. Basically there's a metal bar which slides under the mattress and 2 long fabric straps with a plastic disc on the end which slides up and down to adjust depending on the width of your bed, and is then held in position with a plastic clip which is quite sturdy. We used it on a caravan bed which was narrower than a standard single, and it fitted fine. The bed was against the wall, and after adjusting the length we jammed the plastic disc down the side of the bed base between the bed and the wall, then put the mattress back on top, checking that the rail was right at the very edge of the mattress with no gap. I don't know how it would fit if the bed was not against the wall and can not see how this would be possible, so presumably it's only suitable for beds which are against a wall.
There are two clips on either side of the guard which release it to enable you to fold the side down. However as there wasn't the room to do this in a small caravan bedroom we just lifted our granddaughter over the side. This wasn't a problem at all.
The rail is very sturdy, very good quality and very well made, and if fitted correctly does not move. However, I would recommend checking it is very well secured and properly fitted regularly as ours became dislodged at the head end of the bed after the bottom sheet had been rearranged. Unknown to us one of the clips had slipped up from down the side of the mattress, and our wriggling granddaughter had managed to push it away in her sleep and rolled down the side of the bed between the guard and the mattress, and was lying (still asleep) down the gap with her head resting on the metal bar that slides under the mattress which had pulled out from underneath it. Luckily her mum was sleeping in the same room and always sleeps with one eye open, so thankfully she came to no harm, but I can't stress enough the importance of checking the guard is properly fitted at regular intervals, especially if the mattress has been moved for any reason.