I used combank/comquest for step 1 and then used both and usmle world for step 2 and did 150 points better. usmleworld was certainly helpful but i used it until about a month before then switched to only combank/comquest. if money is no object i would say get it and use it for the explanations. if it's a choice between one or the other than go combank/comquest. just my opinion and anecdotal evidence, good luck with step 2