These plants are a real gem and I think they're underappreciated. Bees love them and they create a really brilliant display when grown in a drift. People often clump them but I don't think this is the best use- they merge very well with other plants as their flower spikes to a good 1 meters- whereas their foliage remains quite low to the ground. I grow mine zigzagged through a border and it creates a brilliant effect.
Very little care needed. Make sure they're not left to dry out too much as this will inhibit flower growth. They can be divided either after flowering or in spring. Be aware they will spread a little!