I am still making my way through my stack of protein that I have bought and have decided maybe it is time to get one of those protein shaker cup things.  I know what they do and what they look like but the few stores I have remembered to look for one at did not have any!  Where the heck do you get these things?!  And is one kind better than the other?  I see some with strainer lids, some with wire coils at the bottoms and some with wire balls inside (like the  picture above).  How do you know which one to get?