(1) I have not spoken to many clerks, but why would First Class LETTERS have a provision for a non-machinable surcharge if something like a chip could not be sent first class letter rate? Thus I don't see why POSTAGE DUE could be tacked on later unless the resulting mailpiece was MORE than 1/4 inch thick.

(2) If you look at my post and picture in this thread, you'll see that I carefully sandwich the chip between strong cereal box-type cardboard, tape that securely, and tape that chip "package" to paper inside the envelope. So it is unlikely to be damaged by the post office processing machines. And I only send cheap chips that I have a lot of that way.

Robt.