TN application/renewal by mail

The general trend for applying and renewing TN status seems to be by traveling back to Canada and going through the process again at the border/port of entry.

I was wondering if anyone has had experience using the I-129 form and if they could share how straight-forward or difficult that experience was.

I appreciate the input! Thanks.

USCIS is better. Its more predictable. USCIS deals with immigration matters only. CBP deals with customs and immigration. USCIS adjudicators, aside from senior Free Trade Officers at some Eastern Ports, have a more sophisticated knowledge of the rules.

I will be trying to extend my TN visa by mail. I am having a tough time finding straight forward info on the process. I have completed the I-129. What additional documents should be sent in? Can these be photo-copies? What address is this sent to? I am finding conflicting addresses online.

Thanks!