I bought the 30" Designer Coco Rail Mount Planters from Walmart 3 years ago and could not be more pleased with how well they have worked for me and have stood up to the elements.
The planters are made of metal that has been painted black and they came with the the coco fiber liners all ready in them. They attach to the railing of a deck with a mounting bracket. The bracket has a nut that slides so you can adjust the size to fit most rails and then it has a screw that you turn to tighten it in place. You then simply fill the planter with dirt and add your favorite plants to it. The coco liners hold the soil in place but allow proper drainage to occur as well.
The coco liners in the planters have lasted three years which is a very long time for that type of product but I think they will need to be replaced next year because the color has faded and they are starting to break down. We keep the planters out all year long so they are exposed to heat, cold and everything in between yet they show very little in the way of chipped paint or rust. We keep flowers in them from Spring to Fall each year but in the Winter when there are no plants in the planters, our cat uses them to lay in and sun himself. They support the weight of the dirt in them combined with the weight of our cat who probably tips the scales in the 15 pound range with no problem at all.
The price on the planters was reasonable and I have been extremely pleased with how good they still look after all this time. I recommend these as a great buy.