If you grow from seed or buy plants and want to use them for cut flowers, check seed packet or plant tag for the height, since there are also short varieties. You can find these as 3" perennials in spring at Coleman's in Ypsilanti.
Like so many nice cut flowers, balloon flowers need to be staked. If you don't stake them before they fall over, the stems turn upward and they will look goofy if staked up afterward.
Balloon flowers are not hard to grow but do have a few quirks. They are taprooted and do not do well (i.e. often die) when moved, so site them thoughtfully. As perennials go, they are slow growing and may take 3 years to reach full size, so you have to be patient. However, like many slow growing, taprooted perennials, they are long lived - you will have them a long time. Lastly, they disapper completely below the ground in the winter and emerge late in spring, after nearly everything else is well on its way. When they finally come up the shoots look like tiny asparagas. Because of this late awakening, you need to mark or somehow remember where they are and not assume they have died or that you somehow left an open spot in your perennial border.
Platycodons share all these quirks (aside from looking like little asparagas when they come up) with Asclepias tuberosa which blooms at the same time. They also look nice together*, making them one of the "plant marriages" you read about in the perennial books.
*Blue balloon flowers look good with orange asclepias, the pale pink ones will look terrible.