Sky stream has no local-storage for recordings, therefore it doesn't record at all.
Instead, you get limited “Cloud Recording” capabilities, with the device supposedly being able to record up to 1,000 hours “to the cloud”, and then stream them back to you on demand/playlists.
It relies on streaming from 3rd party apps like BBC iPlayer My5 and Channel4, each with its own content expiry rules.
It's missing a number of freeview channels (all of which are now available on the VM Stream box)
The Sky Stream puck will stop working if you unsubscribe from Sky – even the 3rd party apps like BBC iPlayer won’t work anymore.
It does have the advantage, when you’re watching a live channel, you can always pause and resume the live broadcast. Starting over, however, depends on the channel – some have that function, and some don’t (much like VM Stream)