They can be used, but are basically disposable. There is liner that wears away or can get cracked after a while imparting a "steel" taste to your beer. They serve a purpose and may actually be the best thing for you right now so don't let this discourage you.
HB99 uses them and has quite a stash, so they can't be all bad. If you have a small space and want to keg and don't mind the negatives then go for it.