I've been doing the Body by Science big 5 protocol with my girlfriend for over a year. Here are my thoughts:

First of all, the book is called Body by Science, but I think it should really be called Body by Philosophy. It takes more a first principles approach, taking what we know about biochemistry and biology from science, and then extrapolating a proper workout routine from that.

If it were truly Body by Science, it would take the next step, and correlate the hypotheses it makes to actual studies of the workouts it recommends, but it rarely does so.

This leads to a lot of wrong hypotheses. For instance, it says that one set to failure gets 100% of the strength benefit of the exercise - In testing, it only gets about 60% of the benefit.

However, even if the first principle approach leads to a lot of errors like the one above, it still manages to be "kinda" right... it allows for consistent strength gains.

In this sense, the protocol is about as optimal you can get for time (15 minutes a week), while still making consistent gains. This is what really keeps me going with it. It's something I know I can commit to for the rest of my life if necessary, and it's something that I could easily convince my girlfriend to start (and stick with for over a year now).

If you're looking to minimize time while still becoming stronger, this is the protocol for you.