I have ADHD-PI and am medicated. I too believe this cannot substitute medication in anything but less severe cases (if that even exists), but I cannot overstate the importance and usefulness of coping mechanisms and attention training. It really defines to some extent whether medication is necessary and in which form (only working hours, all waking hours, etc). Now, granted, for some even building habits and a routine is impossible (like me sometimes too), and then medication fixes some issues and one starts to almost automagically create habits and routines.
I've gone years unmedicated when I had a less demanding and more lax work environment and daily focus meditation has helped a great deal. If I'm not mistaken some video games have also vastly improved and kept alive quick reaction times and delayed reward mindset - stuff that this game seemingly also does - training being less impulsive and overriding other, negative habits.
It makes perfect sense - video games can release high amounts of dopamine on demand, while in our daily lives we lack release in key moments. Synaptic plasticity, learning and memory is dopamine dependent. In a dopamine deprived brain, if timed correctly, these sudden releases can be extremely habit-forming and beneficial.
I've read through their whole website and nowhere is mentioned that this is supposed to replace necessary medication. It's simply another tool in the toolbox, and as such should absolutely not be disregarded. I can 100% see this being extremely helpful and would love to try it out - unfortunately the apps are only available in US app stores.