Just looked at the T&Cs of that site to see if they offer any kind of guarantee, and their T&Cs are positively worrying!

A choice extract:
"If Royal mail lose the item (after the 15 working days have gone classed as lost) this is beyond our control .We cannot issue a Refund as you selected this delivery option and you should be aware that this option is not a guaranteed delivery service (As per Royal mail)"

The punctuation and capitalisation of that paragraph is actually relatively good!