I’ve got it as a neighbour gave me a friends and family voucher, so it was just the cost of the install. I only have the single box
You can download recordings to a tablet to watch offline.
You can record more stuff at the same time (I think 4)
There’s a picture in picture preview of the channel you’re thinking about changing to (on the old sky box, you used the up arrow button to see what was on the channels around your current one, that now has a tiny preview)
The red button stuff on BBC sometimes seems to make the box hang and require a reboot
There isn’t a “+24 hours” button on the Programme guide which whilst it doesn’t sound too bad, is quite annoying.
I wouldn’t be paying Sky an additional £12/month for it