It is good if you do not have anything else. I.e. if you have Delphin, it has this attachment. It works the same way. It will "beat" the mattress and suck in the dust that comes out. But this only work for one or two things, maybe your sofa as well.
But, if I can only buy one thing, I would go for a good vacuum cleaner. Why? because, a good vacuum cleaner will do a decent job with the mattress (nowadays we also use mattress protector), the sofa, the nooks and corners, the floors, etc. An entry model for Dyson is only $600+... and you wouldn't want to end up with many items.