Domestic:
When USPS raised their rates on Priority mail to the ridiculous prices they charge now, I was forced to make First Class Package an option for small/non-fragile items.
I have shipped approximately 50 packages by First Class Package and they have already have one lost package. This exceeds my total losses with Priority Mail covering the last TEN YEARS and some 10,000+ packages.
First Class Package is a garbage, step-child service. Only use it to ship low-cost items that have profit sufficient to cover the replacement item's cost and cost of re-shipping. Any other way: LOST PACKAGE = LOST MONEY
For reference everything was shipped with electronic labels. Dropped off/or picked up by USPS and a receipt received with tracking numbers/total number of packages, etc.
International:
Here's lower cost, higher reliability way to ship internationally than USPS First Class Package:
1)Put your item(s) in a mason jar with a shipping label.
2)Seal it tight.
3)Make your way to whatever ocean is closest to your shop/home.
4)Drop the mason jar in the ocean.
5)Wave goodbye.
6)Your item(s) will get there - somewhere - someday.