Never used Big K but I can highly reccommend FogonUK. Much cheaper if you can pick it up from Middlesbrough or if you place a big order. I haven't used it on a Kamado yet but others have with good results.
I had mine from https://www.fogonuk.co.uk/ several times (only £10 per 10kg when collecting in Middlesbrough), can't fault it. I love a good bbq, but never tried a kamado yet. How did it go for you?