Yeah, Kaplan doesn't give you the "Academic Average" and "Total Science." Not sure why, but its not a big deal when you have all the subscores for each section and can see where you are strong and where you have to improve. The OAT does not simply average the scores together, I think they weigh some higher level/deductive reasoning questions more than simple recall questions, and this reflects in your TS score. I read that somewhere (opted.org or the official OAT score sheet explanation). My own TS score was not an average of all the science subscores, there was a difference of 10-15 points.
I thought that the practice tests were excellent preparation for the actual OAT. The questions were similar or a bit harder than the OAT. Not only are the questions good examples, but its great to learn how to build stamina and figure out how fast you have to read (RC), solve problems (QR), and skip what you need to in order to move on to other questions you can answer faster (all sections...but definitely QR).