Conundra math app is similar to the game 23 in that a target number is given and students use the four operations to figure out a number sentence that equals the target number. Students can change their number sentence by using the "undo" button, which they liked.
I had a couple of sixth grade students use this app today. They liked working on the problems together and that they could go back and change their original equation. When they complet a round of the game the screen shows the equations that they wrote during the round and it gives them a statement of how many equations they wrote correctly out of the number of equations they attempted. They are also provided with the average score of their games playes and their percentile average.
One frustration I see with the app is that when the equations are presented at the end to the students they are presented the way the students solved the problem. For example 9+3x2≠24 but when they did this on the iPad the problem is done one step at a time, 9+3=12, then they work with 12x2 to get 24. When written correctly to get 24 it would have to have parenthesis (9+3)x2=24 but this is not they way the equation is displayed on the final summary screen.