I doubt it even does that.
The moment you buy something, you have to give up a name (which can be gleaned from your billing info), a physical address, an email addy, and often a phone number. Sure, you can go to outlandish lengths to scrub a lot of that info (pre-paid debit card + burner phone + rented mailbox + quickie gmail thingy), but unless you feel like living as if you're in a witness protection program, odds are good that your information will make it out there to at least one retailer. That retailer in turn bundles and sells your info and poof, there you are, ready to be traded like everyone else. I suspect that only the really massive corps like Amazon won't bother selling your info to anyone else... at least that I'm aware of.
Think of it like DRM and how well that doesn't work... then realize these folks are basically selling you a means to DRM your info.
So, unless you end up living like a hermit and buying everything in-person with cash, there's not much these startups can really do to help you stay private (at least that you can't do on your own to an extent). Now if you want to pollute the data and jack the signal-to-noise ratio top the point where no one knows for certain if you are really you, that's a whole different story entirely...