I did not get it as a dedicated home Internet package, but bought an unlimited 4g sim only contract for £20 a month with 30 day cancellation (and then used software to bypass tethering limits and link up to my laptop etc).
Even in London where it ought to be super fast, I found that even YouTube was pretty much out of bounds. I know others have had better experiences, but mine was a download speed of 1mbps if I was very lucky. I think that three offer the data levels they do because they are far slower than the competition and it becomes swings and roundabouts. That is my experience at least.