UWorld's full of ****, no offense to them.
They curtail their QBank at a length of 2145 questions, and then they charge you extra for their biostats package (which is just additional questions, minus the good explanations), as well as for the UWSAs, which are "just like UWorld." That's not to mention, the QBank severely lacks in the biostats department, so it's almost as though they removed a percentage of that subject from the actual QBank just so they could charge people for the external package.