Some say they’re good while others are doubtful . I’ve opened accounts with several, but only paid for one ,Cognifit .
I think the games are better on Cognifit . However the scoring system can produce widely changing cognitive domain scores,up or down, within a very few training sessions, that don’t make sense .
There is even some conjecture that board games like chess don’t improve anything other than making you a better chess player. I only play Sudoku but not sure if I’ve noticed any changes other than that I’m a faster solver.
I was part of two studies testing the efficacy of brain training games. Shortly after starting my first study, I stopped having positive symptoms. They haven’t come back in three years. Could be coincidence. Could be that the games helped.