I've gone through a wide variety of sleep cycles due to different circumstances in my life. For about four years I worked two jobs that were spread out so that I basically had to sleep for 3 hours at night and 3-4 hours during the day--after a few weeks this sleep approach worked just fine. I wouldn't say it was better than what I do now (6-9 hours in one shot), but it certainly worked--and I would get "tired" at the appropriate times.
Personally, I think the most important part of sleep is consistency in that you train your body/brain giving both expectations about how much sleep will occur and when it will occur. There are periods of my life where I functioned just fine on much less sleep than I get now, but the waking up "process" was somewhat less pleasant. On the other hand, oversleeping leaves me more tired than I ever was in the first place.
From what I understand (and I've found this to be true in my experience), an entire "full" human sleep cycle (i.e. a trip through all the sleep stages) lasts roughly 3 hours. Therefore it seems logical that one would be best off sleeping hours that are multiples of 3 (3, 6, or 9). Basically what you are trying to avoid is waking up during the REM or Deep sleep cycles--instead positioning your wake-up during the 90-110 minute Light sleep cycle that begins each 3 hour cycle. Obviously this is pretty hard to gauge on your own--but by using the simple test of "do I feel like crap?" vs. "do I feel amazing?" when you wake up one can learn much of what sleep is best for them.
The Biphasic sleeping style described by the OP certainly sounds promising--and I've known a variety of people who "break off" a scheduled nap with great success. That said, I don't think I could ever pull off a schedule like that--just because things spring up in my day to day life that would most likely make me miss that all important nap. Plus, I just can't make myself believe that I'm going to jump out of bed for 2 hours and be insanely productive just to take another nap (I kind of enjoy being lazy and groggy for a while when I first wake up).
Obviously the circumstances of your waking life will almost always threaten/interfere with sleep schedules--but if you have the freedom to experiment and discover your perfect sleep schedule I definitely could see it having amazing effects on your life--plus... let's admit it, sleeping is kind of fun. :lol: