Just managed to get this for £19.99 but I had to use Edge, if I went via Chrome, Firefox or Safari, the price was higher.
I did get the original link via email but used Google to link to the UK site, I'm also using IE11, price still @ £19.99 for me.
It's been changing between £29.99 and £34.99 (F5 Bingo) However, even at £29.99 when it's in the basket it jumps to £34.99 @clay , not sure how you got £19.99 (email specific link for you maybe?) but I've had other Mods check and we all get £29.99 changing to £34.99 I'm afraid
Shows £34.99 for 5 devices. Been using Sophos Home (free) for a while now without issues.