Your body can dissolve any multivitamin and it's a lot better to take one which has a chance of absorbtion.
I don't notice anything from MV's, if i need a pick me up i get some Behepan, 1000 X your daily need of vitamin B12 and increase my caffeine intake.
It's also a lie that your body can't use synthetic vitamins, apart from vitamin E (the absorbrion rate is around 30% for that and no one really knows why) it treats them the exact same as if they come from any other source.
So overdosing them isn't a bright idea either, vitamins in too large amounts counteract the minerals and even each other and a too high intake can actually lead to vitamin/mineral deficiencies.