On Seaborne Encore,
1 device / guest is gratis, but limited access(streaming is blocked, international texting is limited, some sites blocked unless using VPN). Paid service is about $20/day (price does decrease as cruise days pass, despite what staff will tell you at the beginning) and includes 4 devices, which can be any 4, including friends/ family (I shared with friends in another cabin), as long as total devices does not exceed 4 at any given moment.
Be aware that it is an upgrade, so the purchaser loses his gratis access(he doesn’t get 4 streaming plus one surf access, only 4 streaming), which sucks.
The streaming is not significantly faster than the gratis access, only unblocked by Seaborn.
Hope this helps, I couldn’t find this info anywhere before our cruise.