The only disadvantage I see to that is thet when you thaw and re-freeze something, it diminished the quality and nutrition of the food, I believe, thus making it necessary to feed more to attain the same nutritional value, THUS creating more waste. Something about it breaking down the cell walls and forming ice crystals in the tissue, but I could be mistaken.
Of course it makes sense though since PE mysis is supposedly the most nutritional Mysis you can buy, supposedly because the mysis are flash frozen alive, minimizing tissue damage.
I would think that thawing only what you need then straining it before feeding is the best approach.
But if it works for you, then who's to argue.