They are fine when it works. But my package was not delivered or attempted to be delivered by Royal Mail. Consequently sitting in the sorting office for four days during a heat wave. I’ve contacted BMI about this 3x they said don’t worry it’s fine to use. Really?? Then why do they go to the trouble of a 24h temperature controlled delivery?? Then they said the package is not their responsibility once it has been dispatched. Which is absolutely not true, it is the retailer’s responsibility to ensure that the items arrive as sold. What concerns me the most, this isn’t a pair of shoes, it’s a medicine being injected into the body and they could not care less the condition of it. A pretty major red flag.