Short answer: they can work very well, but they are not magic. A built-in reservoir is useful when it is designed as part of a real self-watering system, not just a plastic tank hidden under soil. The reservoir stores excess water, and a wick or capillary mat pulls moisture upward as the potting mix dries. For urban gardeners on balconies, rooftops, or small patios, this can reduce watering from daily to every few days, limit runoff, and make better use of limited water.
The gimmick version appears when the reservoir is tiny, the wick is weak, or there is no overflow. A sealed planter with no drainage path can drown roots, encourage mold, and become a mosquito nursery if water sits exposed. Many cheap “self-watering” boxes hold only a cup or two of water, which does almost nothing in a hot, windy city microclimate. If you use heavy garden soil instead of airy potting mix, capillary action often fails, leaving plants either soggy or bone dry. And no reservoir removes the need to fertilize, prune, or check for pests.
To tell whether a planter is genuinely useful, look for a separate water reservoir below the soil chamber, a fill tube, an overflow hole, and enough capacity for the plants you want to grow. Vegetables and thirsty flowers need several liters of reservoir space, while herbs and small ornamentals can manage with less. A fabric wick or broad capillary mat works better than one narrow strip. UV-stable, food-safe materials are important if you are growing herbs or vegetables. An aeration gap or drainage layer also helps prevent waterlogging.
Built-in reservoirs are best for herbs, lettuce, chives, mint, peppers, cherry tomatoes in large models, flowers, and small shrubs. They are less ideal for cacti, succulents, rosemary, lavender, and other plants that need very dry roots. In rainy seasons, the reservoir can overflow; in extreme heat, it still needs refilling. They work as a water buffer, not autopilot.
Verdict: urban planter boxes with built-in reservoirs are not inherently gimmicky. They are a practical tool when engineered well and matched to the right plants. They become gimmicks when sold as “never water” miracles with tiny tanks and poor wicking. Choose a quality model or build one carefully, use proper potting mix, and check the water level regularly. Then the reservoir can genuinely make container gardening easier, cleaner, and more water-wise.