I own both the Brenner and the Lange pharmacology flashcards.
I first purchased the Brenner ones. After having studied them for a couple weeks, I realized they were very boring, as they were just a word on one side and lots of generalized info the other. Not to mention, nothing on the info side is refined toward the benefit of USMLE study. For example, for the psychiatric drugs, I'm pretty sure 3/4 of them would say "sedation, decreased appetite, loss of sexual interest" etc., without ever really cutting to the chase.
Then I purchased the Lange cards because I was getting impatient about learning pharm AND First Aid had them listed as fairly strong in their list of resources. These are MUCH BETTER, and they're actually vignette-style, so each one is, to an effect, like doing a form of practice question. And when you flip to the info side, there will be certain terms in bold that are more important than others. Finally, in the first couple intro cards, the authors talk about how they specifically tailor the cards for USMLE Step1 study. I found the Brenner cards were just dry and mindless and I didn't retain anything by having used them. The Lange cards come with tree-algorithms for the drugs as well, which the Brenner cards don't have. To this day, I still visualize the algorithms for many of the drug categories, and they have helped out a lot.
Bottom line: don't get the Brenner cards. Get the Lange.