Is amazon fba worth it? how common are horror stories?

I have been shipping myself for the last year and done 2 mil in revenue, however the cheapest way to ship is post office and ever since they switched to ground advantage my on time delivery has dropped from 95% to 74% this week because of the xmas time. I am thinking about switching to fba, my products are all under 4 ounces and take very little storage, how are the fees compared to the post office, also I figured because its prime I can charge more as people want stuff fast is that true? Also I seen horror stories that amazon loses stuff in the warehouse, I have also seen videos about amazon employees getting caught stealing items. How common is this?