So, I filled out the info and paid ~$35 for a 5lb box.
Got an email Monday morning with a PDF of a FedEx label. (I thought I was getting a box and a sticky label, but I didn't really know).
I had similar size Amazon box lying around (actually like 5) that was similar to the LARGE box in their description.
Packed it up, brought it over to the FedEx office location. Made a copy of my license to put in the box for the FFL. Taped up the box and brought it up to the counter with that shipping label in hand. The girl at the counter pulled out one of those sticky clear envelopes to put it in. She slapped it on, printed out another barcode sticker and handed me my tracking receipt.
It shipped as next day air, so as long as it gets there, I'll definitely use this service again as the cost is half what my FFL wanted.