Belgium, not the Netherlands. They seem to be selling refurbished ex-lease bikes, together with surplus stock of end of line models.
My anti virus flagged the site as being potentially dodgy, although I'm not saying it is - it could be a false flag. The site gives a Belgian VAT number which checks out as valid. Having said that, the address given (Hey-endlaan 36) is for a residential property in a village just outside of Essen.
Bear in mind that if buying a bike from Belgium there would be import duty to pay when bringing it into the UK. Technically.