I have both and read both along with FA and my concurrent path classes. Pathoma is high yield PATHOLOGY of systems (with a little pathobiology). Rapid Review is more than that. It is integration of pathology with physiology, micro, genetics, pharm, biochem, all the subjects of FA basically. It teaches you to think like a question is worded on a step 1 test - secondary and tertiary. Also, RR covers chapters like path of genetic diseases, nutrition, etc. Yes, you can get most of that in FA but it is not as well integrated. I'd say RR gets you to think like the test (equivalent in just doing a bunch of questions if that's how you learn best).
When it comes time to cram, I will be using mostly FA and pathoma for review just because it is shorter (although the margin notes and boxes in RR will be a def must).
Also Goljan audio is pretty cool. If you listen to the audio you will see how RR is written in a similar way - multi-step analysis of the problems. I don't want to argue with anyone since I think all are great products (just look at the rating RR got in the back of the new FA and you'll understand) but just understand that they are not equal.