Hey Moo Cow,
Generally in Deck-byilding games you will play with your hand private and it's perfectly acceptable to discuss who should get the benefits of effects and what you plan to accomplish on your turn.
I have not seen a co-op deck builder where players play with their hand visible. It can lead to "alpha" players taking control and making the experience less enjoyable for everyone else. If a player wants to play with his hand visible that's up to them.
Harry Potter Hogwarts Battle works differently. Each player’s hand is on the table during other players’ turns, visible at all times. There are cards and effects throughout the game that will “check” what’s in someone else’s hand. For example:
Spoiler (click to reveal)
Harry’s Invisibility Cloak can save him from damage during other players’ turns, and George and Fred Weasley look to see if any other players are holding other Weasleys when they’re played.