Hi Renee,
I do lots of international ordering but have never ordered from that site- they look good though- they have physical stores in the UK and have been around for a long time.
Their shipping fees to the USA are 19.99 pounds which is a little pricey but I usually pay $40 to have boots shipped to Australia so IMO, it's not so bad and probably a pretty good reflection of the actual cost to the company.
They'll deduct VAT (sales tax) from international orders so the cost of the boots will end up being less than what's listed.
If you are pretty sure of your size then I'd go for it!