Hi @Anonymous User
Unfortunately you can't pre order the smart stick on the nowtv website and will have to wait until the 26th of February 2018 for the official release date.
Alternatively you may be able to pick one up from Argos on Monday (subject to store availability).
I don't know how accurate this internet article from Gizmodo UK is, but according to the article the NowTV smart stick will be available to purchase from Retailers Argos, Tesco and Sainsbury's tomorrow the 23rd of February and direct from NowTV themselves on the 26th of February.
Suppose we will find out tomorrow,if the article is accurate or not