As Twitch is currently only shows prices in $ that you will also get charged both a conversion fee and a higher price
on any DLC/Crown packs bought through Twitch alongside the ESO 'Free' Twitch Oroborus Crate Promotion.
Depending on the current exchange rates this can vary but it is around a £2 increase on a 750 crown pack compared to the ESO store
I would hate to see the increase on both DLC's and the 21000 crown pack prices although I suspect it would be nearly double the cost!
(FAO ESO Staff this has also been reported under: Ticket #180628-001777)