(bumping this older thread because I have the same questions, and maybe the OP has returned and can offer their opinion based on recent real-world experience)
We're headed for the UK in late June/early July for 3 weeks. We will start in London, wander around a bit of nearby England, then head north, spending a bit more than half our trip around Scotland, including some of the more far-flung islands (Lewis and Orkney). Using public transit in London, and much of the other parts by driving. We will have a dedicated GPS with maps of the UK as a primary navigation device while in the car.
I'm interested in options for data connectivity while out and about (we don't care about phone calls, only data). Yes, I know many hotels will have free wifi - I get that. On recent trips we have found that having good data connectivity all day makes a big difference - and no, I don't mean because it allows one to waste their day Facebooking when they should be actually experiencing life. Previously I would have scoffed, too, but now I got religion...
On our last trip to Japan we rented a "pocket wifi" device and found it utterly liberating. The connectivity was super fast, rock-solid reliable, and was available almost everywhere (we lost connectivity briefly in longer rail tunnels, but otherwise were always connected while zooming along at 150 mph on the bullet trains - only while hiking in remote areas did we fail to get a connection). We used multiple devices (his and hers iPads) for everything from picking restaurants to navigating subway systems, to learning about the places and things we stumbled across. It allowed us to navigate on foot everywhere - underground (Tokyo has a vast maze of underground pedestrian walkways), on subways, though tiny back streets, even on paths out in the countryside (thank you, Google Maps) - it made everything almost too easy. It allowed us to buy tickets to sites while we were en route to them, find out opening/closing hours for obscure attractions, get tips from others to make the most of our time, and a thousand more things that made our trip much easier and better. Nearly every day we would turn to each other, amazed and delighted, and say "wow, I'm never going to travel without one of these again!"
In Japan, it could not have been easier. The service delivered the device to our hotel so it was waiting there for us on arrival. Dropped it in a mailbox in a prepaid mailer at the airport as we left. About a hundred bucks for 2 weeks, an incredible bargain in my eyes.
I don't expect wifi across the UK to provide quite the same speed (our device in Japan was rated at 75 MB/sec, and seemed about as fast as my workplace's super-fast wired broadband) nor coverage to be as broad (I'm realistic - I expect cellular coverage will be sparse at best across a lot of Scotland, and spotty in many other places). Still, I'd be happy to pay for a device that would give us connectivity throughout the trip (allowing for those gaps).
I'd be thrilled to find something similar for our UK trip. Anyone have experience and/or recommendations? Thank you!