The full rules of this variant can be found here but basically the tiles act as wild colors for completing rows. There’s a bit more nuance than that but the rules are short and anything I say will basically be copying and pasting.
The worth of grabbing Joker Tiles comes down to how much you value end game scoring. These wild tiles do help players complete larger rows and harder to come by colors much easier than without, but players will be dinged as they cannot complete the five of a color bonus (if they used a Joker Tile). If you’re playing an aggressive, fast-paced game that probably includes hate drafting, this isn’t as big of an issue as players shouldn’t complete many, if any, full sets by the time the end game is triggered. For other scenarios however, the tiles will have an implications on scoring.
Joker Tiles also do not reenter the general supply like other tiles do. Since they are being moved to the right side of the player board, the amount of Joker Tiles available will become less and less as the game progresses.
The inclusion of the Joker tiles makes the game slightly more easy for players when they can utilize them as they can complete their rows slightly faster (especially if the color they need is not coming up) but that is at the risk of losing additional points at the end of the game. There is an increase in decision-making as players now have to weigh the completion of a row against the quickness of completion by using a tile. In games where players are familiar with Azul and rush towards the end, the Joker tiles can basically break the game. Games will end far quicker and with far less points as players try to end Azul in as few as turns as possible, which is easier now with a Joker tile.
I think not being able to score the ten point bonus is huge as it can easily sway a game in one direction or another. In my experience, games tend to end quicker than usual when using the Joker tiles as it’s easier to finish rows. This means that most players are not getting a chance to finish all colors and/or columns so the player that really utilizes the Joker tiles to their full potential will be in an above average spot to win the game.
The new tiles impact the variant board more than the original board in my opinion as well. It becomes much easier to navigate the open spaces with a ‘random’ tile that can come into the mix.
The randomness of the tiles will also change how they’re used. If they’re seen in the beginning of the game, players will react much differently than at the end of the game where they might snatch them for completion purposes. In the beginning, players are still trying to decide what route to pursue and a Joker tile might sit until the game forces a player to take them.
All that being said, I wouldn’t bother with the Joker tiles unless you were a completionist. I don’t think they made Azul a better or worse game but they did change how the game was played. I was not a fan and don’t see myself using them again as I think they remove the basic strategy of trying to add a full set of colors to your board. They are pretty and fit the motif that Azul has created but I fail to see the value they add to an already highly competitive game.