It will not be synced. Each device receives its own data stream. I experimented with this in the past just to see what happens. It’s hard to start each one at the same time, so one would be a little behind the other. This depends on which one you pressed the play button last.
With a little playing around, I once managed to press the play button on both devices at the same time, and I got the two streams to play as if synced. But that was only because I started both simultaneously.
To explain this another way, if two people in your household want to watch the same movie, but on two different devices, there is no problem with that. If one happens to start watching five minutes after the other, their entire movie will be played, from start to finish, five minutes behind the other.
One last thing, even though one account can have up to six user profiles, only a maximum of three devices can stream channels simultaneously on one account. It’s not necessary to create user profiles unless each family member wants to keep their own saved DVR programs separate from other family members.