This was the first of Unlock series that got me hooked onto the rest. I really like escape rooms and found this a really good alternative. You need to down download the free app to play which keeps time, score as well as providing the ability to give you clues.
I have found the series very good, the puzzles are clever and flows well with the game theme for each box (only one I have played which I don't like).
The only downside is that you can only play it once.
Another comment is that many of the boxes will recommend 1-x players. I have found most of these games work well as with 1-2 players only. more than that and it actually becomes much slower and other players end up sitting around when they can't see the cards well.
Unlock! games pack a great level of challenge into a small box with a small pricetag. Nothing gets destroyed so after you play you can pass the game on to a friend.
The Formula is a great start to the series.