I agree with it to an extent. Think about it, if you are able find what your child cares about, you can use it to help them think about and monitor their own behavior, while acknowledging the consequences for their actions.
But what happens when your ADHD child doesn't really have a "currency"? What happens when they don't have genuine, deep connections to objects or material items? What happens when you finally find their currency and after a couple of attempts to control their behavior through restricting their currency, they loose interest and don't care about it anymore? Or what happens when that currency is either reading or playing outside?
Let me share with you some stories of myself when I was younger in an attempt to explain what happens when you try to control behavior through a child's "currency"....
When I was around 7, my mother started to require my participation with the family chores. I was supposed to feed the dog and empty the dishwasher. She thought, as many parents do, that an allowance would motivate me and make me want to complete the chores in a timely manner so I could do fun things, like see a movie, with my friends. However, she did not bargain for the fact that money didn't really interest me and my desire to go out and do fun things did not overpower my disinterest in doing my chores. She then tried a sticker chart to visually show me what I could earn if I did my chores. She changed the currency to a toy, one that I had been very vocal about wanting. But as soon as that toy became the prize for doing my chores, I didn't care about it anymore. She took it one step further and said that for every chore I didn't do, I would have to spend 10 minutes in my room after school. No problem!! I loved reading and would gleefully curl up with a book, thus avoiding my homework at the same time while serving my punishment. Pretty sweet deal if you ask me!!
To be honest, I never really had a material currency, and if I did, it was watching TV after school to decompress and re-charge my dopamine and serotonin levels. But I could even go without TV since reading did the same thing for me. What did work was saying that it had to be finished by the time we left to go somewhere. One of my OCD tendencies is to obsess about the time we needed to leave. If you say we have to leave in 15 minutes, we need to leave in 15 minutes and any later meant my anxiety would go into overdrive. If my mother said my chores had to be completed before we left and we were leaving in 15 minutes, you better believe I would get those chores out of the way before we left.
My advice is to not too much stock in trying to find your child's physical currency, instead, try to figure out what they focus on and what needs to be "right" in their little internal world for them to feel calm. As weird as it sounds, you need to use that need to your advantage. If your child is obsessive about rules, make it rule they must do BLANK. If they love going outside to play, they need to make sure that BLANK is finished before this.
This can even work for inappropriate behavior. For instance, my son hates to clean the bathroom floor. I know this and reserve this chore as a punishment to add to his other chores. He has three strikes in the morning and then we start over in the after noon. Strike 1 is a warning, Strike 2 is the loss of his dessert, and Strike 3 means that in addition to putting his backpack away, feeding the animals, doing his homework, and putting away his clean clothes, before he goes to bed that night, he has to clean the bathroom floor. He knows this because it has been a part of our routine for a couple of months now. But, if he started to outgrow this chore and I had to change it, I would do it slowly so he could get used to a new routine and then it would become normal. Flipping out or throwing a tantrum only serves to increase the amount of time he has to help me clean on the weekend.
This can help create a sense of expectation about behaviors accepted or tolerated and also provide your ADHD child with a connection to a feeling or internal checks and balances instead of checking out the entire process all together. And if it doesn't work, you can always keep changing it, trying new things until it does! We are "parenting experts-in-training" after all...its a constant work in progress!