These are often refered to as "hot-weather spinach substitutes" and they all do produce a crop of succulent, leafy, mild-flavored greens in hot weather, although each has its own personality and flavor. In general, greens are best if growth is rapid. Ensure that by giving them plenty of compost, water, lime if necessary, and some midday shade, at least as seedlings.
Greens work well in containers, or those awkward places shaded by other plants or objects--on the east side of a house, or a bed of tall plants. For summer meals, try steaming the day's harvest in the evening while you are doing something else in the kitchen, then putting the cooked greens in the fridge for a quick cold dinner dish the next night, served with olive oil, lemon and salt - a classic Italian start to a meal. Or scramble them with eggs and cheese for a quick frittata.