Mjollnir provides enough IAS on its own to make the orb effective. If you add treads or some other similar IAS item (maybe Midas?), it becomes plenty effective. It's why Mjollnir can be effective on pretty much any hero. Maybe some use it better than others and Lysah already explained why Mjollnir might not be a good choice on a carry Tiny, but pretty much any hero can get their 5k gold's worth out of it.