I've had a MountainHigh portable system for some years now. The big advantage of the pulsed delivery (other vendors have similar) is that your bottle duration is measured in trips, not in hours. It's a real pain to have your bottle poop out on you when there's no convenient place to refill. Also, portable systems are much easier and cheaper to refill than built-in systems. And when you refill an oxygen system, it's a fixed price per refill, regardless of how empty your system is or how big the bottle is. I have a big carbon fiber bottle, and it's great.
As for the "need" for oxygen, it turns out that there is essentially no research in the literature documenting the need for oxygen at low altitudes. My empirical evidence is that the FARs are much too lenient, and my personal physiology appreciates oxygen above 8000. On a long, hot bumpy all-day cross country without oxygen, I'm wiped out at the end of the day. With oxygen, I feel good except for a sore nose from the cannula. And this was true when I lived at 5,000 feet and walked 20 miles per week with superlative pulse and blood pressure. One presenter at Oshkosh a few years back said that four hours without supplemental oxygen was the equivalent of a half hour at 14,000 in terms of hypoxia. In my book, being macho about getting along without oxygen makes as much sense as landing with as little fuel left as possible.
And then there's hydration -- water. For me, hydration means drinking a lot of water the day before so that water can permeate the cells. On the day of the flight, water consumption is sips during the flight. Big chugs of water right before the flight don't do much except exercise the bladder...
What's surprising to me is how much of hypoxia and hydration has to do with comfort and personal performance. Nobody wants to be uncomfortable in an airplane, and nobody wants to fly an airplane poorly. It's amazing how much difference oxygen and water can make, and how easy it is to do.