In the new controlled, randomized trial involving 128 healthy young adults, researchers found that playing Lumosity brain-training games for 30-minute sessions, five times a week for 10 weeks resulted in participants getting better at playing the games. But researchers saw no changes in participants’ neural activity and no improvements in their cognitive performance beyond those seen in controls. The same went for participants who played video games not designed with cognitive benefits in mind.

Source: Lumosity boosts brain function by 0%, the same as normal video games—study | Ars Technica UK

To the best of any studies out there, brain training games are all snake oil. There is no such thing as general intelligence booster, there is just getting better at specific skills because you do them more.