The experience is exactly like shipping UPS or USPS, whichever you choose.  Pirateship is just the seller of the postage.  You print out the label, tape it on, and drop off at UPS or the Post office.

One caveat, do not count on their insurance if you ship a gun.  They use private insurance, and if you read their terms, it appears that they prohibit you from shipping a firearm.  So, if you do so and it's lost/damaged, they'll most likely deny insurance due to shipping a prohibited item.

I ship ammo through them daily, but just expect that I'm self insuring.

dave

Pirate ship is actually not just less expensive, but better in another way. Unlike taking a antique or modern firearm to UPS, where you have to declare what's in the package, you simply weigh and measure the box and print out a label through Pirateship. Drop it off at any UPS or USPS station and have them print out a receipt.
I've used them for about 2 years now since JerryH told me about them and even Priority mail flat rate boxes are cheaper through Pirateship. I think about $1.50 less than direct through USPS.

As for insurance, there are no good choices. Every shipper will run you through the ringer and try to deny any claims. Even when they steal or lose your package they'll try to not pay the claim. So best way is use Pirateship, but send it USPS Registered Mail through Pirateship. I hate USPS, but registered requires a signature and locked storage every time it changes hands. So it means packages are handled by humans who are required to sign for it when they pass it along.