Mike, the £15 let’s you buy it. The 5 years is the standard Costco guarantee. Delivery is by specialist carrier – mine was one man. If anything goes wrong (or if you decide you no longer want it inside 90 days) you can return it to store or they will collect it.
The box / packaging is very large and surprisingly heavy. I always keep such things for TVs and it wouldn’t go in my loft hatch so it’s in the back of a built-in wardrobe.