Although they try to apply consistent customer service across the country, their buying policy seems to be dictated by marketing considerations, and their relationship with certain suppliers. There does not seem to be any processes, where their buying department assesses which products work.
Remember those wrist bands where the manufacturer claimed that they improved balance, and got prosecuted for making the claim? They used to stock those.
Some of their sports nutrition products are pure snake oil. For example the Lucozade Body Fuel Jelly Beans, are exactly the same as an ordinary jelly bean. They are made on the same production line, put in a different packet, and sold at a much higher price as a “sports nutrition product”.
You have to be prepared to take risks in order to fulfil your potential, and fins out where your limits really are. Once you start entering the harder ultras, it is only a matter of time before you get a DNF, and with the very hardest races, you might make a calculation to try them knowing that the odds are against you.