It is cheaper than almost every other computer store in the UK for the same parts, deliver next day and they don't tend to shaft you on delivery cost (if it costs anything at all).
Unless you are near one of the large online shops and need something delivered next day there is no other option than Amazon.
https://uk.pcpartpicker.com/product/Hy97YJ/msi-b450-tomahawk...
https://uk.pcpartpicker.com/product/Y6Crxr/fractal-design-me...
etc.
It sometimes makes sense to spread the parts buy across a couple of vendors to save costs - of course too many vendors and delivery costs eat into the savings. But it's quite rare that I've ended up buying anything other than monitors and the occasional component from Amazon.
Run your next purchasing decision through Google shopping. You may be surprised.