A four jaw chuck only works well if your blank is dead square.
Indeed. I have to square up my blanks with a saw, and then for extra perfection run them through a thickness sander. I am glad to do this, if I need a blank drilled perfectly down the middle. Takes no more time than it does to turn the blank round, and if I'm drilling a big hole, I don't have to worry about collet pressure crushing it. There is still enough meat left on the blank to keep it stable.
As Ed said, this thing would be useful for any blank that had two clean opposite corners, if your corners don't break under the pressure. Sometimes I don't think people appreciate just how violent an act drilling and turning is.
It is wrong to say, as the ad does, that it drills dead center unless the blank is perfectly square. Also, those opposite corners have to be close to 90 degrees or it could shift a little. And the long sides will need to be straight. You're still going to have to clean up even a slightly warped wood blank. On those tommy bar scroll chucks, any wiggling of the blank will loosen the jaws as you go along. You'll need to square up the face that the bit enters. Use a center bit to to start the hole at the very least. It will not do round stock (not enough grab, as was mentioned) and is also, as was mentioned, a one job tool. So is a barrel trimmer, but they don't cost $70, and with PSI's crappy shipping speed on top of that.
If someone's in a hurry and isn't concerned with precision, this thing would probably work fairly well. But you will still have to have the blank sides within certain tolerances.