Honestly an underwhelming investigator. Their ability will almost never see use, their card pool isn't all that great and their signature asset is pretty bad. All of the positive comments about kymani have them using cards that other rogues can also use and usually better.
About the ability: It requires two actions and an overcommit, often by 3 or more, to clean an enemy from the board. So let's take the standard scenario of trying to use their ability to discard a standard 3/3/3 enemy. Most bruiser characters can clear an enemy like this in reliably one action whereas some will require two.
Kymani cannot under any circumstances do it in less than 2, and if they fail at any point they have to reset their attempt. The chance of failure? In our 3/3/3 example, you have to test at a 6 to succeed (anything less is a failure and you've lost two actions trying this). You'll need to score a -1, which will require commits or stat boosts on your part, and this will become dramatically harder on higher difficulties. Now you've spent a lot of actions, cards and resources to dispense something other gators can handle reliably in 1-2 checks. I would go as far to say you should basically never use their ability as kymani is probably better off going after clues.
Trish and Finn are better cluers, Tony is a far better fighter (not even sure you could buld kymani combat oriented), and winnifred is better at being a "Jack of all trades".
Kymani ultimately doesn't add any new playstyles to the game, and all the styles they do use are utilized better by other rogues.
Overall: Probably a D tier rogue. Better than Preston but outclassed by everyone else.