EK and TBR, IMO, are both very useful but serve different purposes.
EK
I took the MCAT twice. The first time, I studied with only EK and got a 12 on the biological sciences section. For the old test, if you absolutely had everything in the EK book down and understood it well, you could get a 12. EK covers the most essential information in the most concise way. EK books cover the least you need to know to do well on the MCAT. There's no fluff. If it's in EK, you need to know it. Period.
TBR
In addition to what you definitely need to know for the MCAT, TBR goes beyond that and also teaches the topics that are either likely, or kind of likely, to be explained in passages. TBR includes a good deal of stuff that is beyond what you really "need to know" to do well on the MCAT. Many people use TBR when they have already done well on EK, and want to rise to the next level.
My observations (regarding the sciences):
1. If you do TBR first, you may run the risk of spending time on very low yield topics while not spending enough time on high yield topics.
2. If you do both EK and TBR, you are probably well prepared.
3. EK alone sufficed for the 2014 MCAT, but only if you really understood practically every thing in those books. You cannot "go through the motions" with EK; you must truly learn practically all of the material in those books. If you just read it and do the questions without making a point to solidly learn the material, you will likely have a bad score.
4. Many people have found a winning strategy in using EK's table of contents as their syllabus, by going chapter by chapter through EK, reading each chapter, doing the questions, and making a list of topics that need more clarification than what EK provided. Then they would search the internet for videos or tutorials on the topics that needed that (30+). That is the fastest way to MCAT success that I am aware of, with one caveat: VR. Neither EK nor TBR or the best for VR (ie CR), as far as I've observed. (Like I mentioned above, if you are able to get through EK quickly enough while doing a scrupulous job, you can then use TBR to take it to the next level.)