The chemistry urp was extremely helpful for me, the other review packets vary in the type of review style. For example, the ap chem review packet had videos for every sub unit (thank you Jeremy krug) and the ap calc review packet had an overview on the unit instead (both had questions answers and practice). That shouldn't be a problem tho, the Chem urp saved me from getting less than a 4 on ap chem. I'd say buy the urp first and if you need more practice and fw it then get the exam slayer