domain:dualn-back.com
I couldn't run the version he used but this site is straight forward.
For the first few days, I struggled. Even 1 was somewhat surprisingly difficult (any mistakes at all). Quickly repeating orders in my mind (starting from top center, going clockwise 1-8) let me go to 5 with the occassional mistake, primarily in cases with repetition. After 2-3 weeks, I can't do much better than half correct at 3 relying on intuition/not subvocalizing previous orders.
Nevertheless, this seems like the most interesting challenge I've applied myself to in a long time. When in flow, it is among the most pleasurable states, akin to soaring among Platonic shapes.
To some extent, I feel more alive/alert/concentrated in general. But I've also started a regimen of basic nootropics besides random bias/placebo.