I'd like a Roku but...
There are two versions available (officially) in the UK, the Roku Express and the Roku Streaming Stick Plus. That's it. The American versions don't officially support iPlayer. It seems that Roku really don't want to bother with the UK market other than via sales of the Now TV box.
Adding insult to injury the Roku web site declares "There's a Roku player for everyone". Unless of course you want 4K and something other than a WiFi streaming stick, in which case you're stuffed.