I decided to start training again so I got myself a set of TRX style straps to use at home. Mainly because I've had enough of lifting weights and don't want to get bulky or anything like that. So far so good. Its a lot harder than it looks but once you get used to stabalizing yourself its all good.
I've used them, and they are a great tool for training.
I wouldn't substitute them for barbells and dumbbells, unless it's all you have.
Otherwise, they would work well by using the db's, bb's, and straps.