Well good for you, I, personally would never, ever, ever use that company you mention for anything ever again, I am even put off by ebay sellers that use that company. As a seller I experienced some of the worst customer service from that company, no apologies, no responsibility taken for anything, no compensation for anything. Final straw - 3 items destroyed in single week, close on £200 value lost. Their excuse - our conveyors are old and sometimes things fall off. Advice - dont put FRAGILE tape on items as they can be seen as a target - their words.
Royal Mail on the other hand have always been fair, taken responsibility and will always pay appropriate compensation - so long as you keep the appropriate paperwork and work within their guidelines.