my Orbital sharpener is gathering dust. i won't "diss" the product; i just found it too difficult to use. not worth the effort. i assume others are quite happy with theirs.
the Colonial sharpeners work great but require a lot of elbow grease. i use mine often.
i just bought the fancy shmancy rectangular one, described above, with the long sharpening stone. it definitely extends the life of a blade if you use it as recommended to keep the blade sharp. because the stone is only one one side as you sharpen, it pays to sharpen, flip, then sharpen again.