I have no idea what I'm talking about in this area, but the only brain games I've run into that I think might actually be helpful are the ones that are somewhat painful, e.g., BrainHQ. Definitely not fun. I start to sweat just thinking about some of the tasks in there.
Probably, no brain games at all boost IQ in healthy people. But some of them definitely help with memory, focus, etc, and I agree that those seem to be the hard ones.
Dual n-back, the general benchmark for these things, is hard. It's exhausting like intricate coding or a tough math proof is exhausting. Certainly I'd be suspicious of anything claiming to do better than that with less mental effort.
