1. This game doesn't train anything, it habituates :P By that i mean it doesn't teach us anything, or make us smarter, but instead it tells us how to cope with certain posed questions. There's a set amount of questions for each 'subject' and each level, and if you just try that subject a few times you'll know where to look, and you wont become better at what mental arithmetic (for instance) but instead you remember witch one to click. That doesn't make us smarter, it just makes us better at doing that test.
A solution to that would be adding a 'random generator' to the puzzles, instead of having like 10 preset ones.
2. It is very superficial; ultimately it will only test one subject. People will find one puzzle at witch they are good, and only do that one.
A solution to that could be to add a rule that you can only do a certain puzzle a few times for each level, or that you have to have tried all the puzzles every level before you advance.
3. the odd-mental out puzzle is badly made. Some time into the game, some of the preset puzzles where impossible and some where offensively easy. Like 3of em wear a green shirt, and one where's a black shirt... you don't have to be an Einstein to figure that one out, in contrast to be able to see that the professor's eye/ manacle twirls around in the opposite direction does take some time and examination.... And loads of other puzzles
As a solution to that, i'm not to sure, but i think that maybe you should balance it out a bit more.
4. Don't call the guides 'Mentals' :P "hi, I'm Patrick and I'm mental" and we are supposed to learn from them?
Since the level you reach depends on how much time you put into this, in the end, this does not enhance mental capabilities, but merely tests one's level of boredom...