The difference in price is the postage. Amazon is free delivery special ingredients is 6.95 plus 2.95 pounds delivery. Same price if your only ordering the one bottle.
I am going to give this a go then maybe try the coconut
I bought five flavours and paid only one delivery charge so going direct was worthwhile for me.
I bought Hazelnut flavouring to make a Hazelnut Stout (l love the Dark Arts version).
I bought Clementine flavouring to make a “Jaffa” Chocolate Stout.
I’ll be interested to hear how you get on with yours and how the coconut turns out.