I purchased a fuel rod during our vacation in August.
During previous trips, I used a 20,000 mah battery bank. It's capacity is huge compared to the fuel rod, but. . . not as impressive as it sounds. My Note 4 has a 3220 mah battery. A bit of quick math might lead you to believe that it would get over 6 full charges from one charge on the battery bank. That is not the case however. It generally was good for about 4 charges from 20 % or so to full. Still not bad, but not nearly as impressive as it's rating implies.
It is convenient to have the battery bank, in that it will charge one device 4 times (not likely to really need that in one day, but . .. ) or charge 4 devices once each (much more likely scenario for a family) and with 2 charging ports, it is possible to charge 2 devices at one time. It also has a charge meter (series of led's) to let you know the state of charge on it, and an led "flash light" built in.
There are down sides to the battery bank approach though. It is large, and heavy, making it burdensome to carry. It gets HOT when discharging, especially if you are charging 2 phones at the same time with it. Because of how much heat it generates, it really is necessary to keep it out of your bag or pocket, so that it can cool down in the air. If you forget to charge it over night, it is going to be of little use the next day. The super convenient flash light somehow always finds a way to turn on in my pocket.
The fuel rod, by comparison, has a relatively small capacity, certainly not more than 3000 mah or so (sadly, they don't make that information available). In practice, it is capable of charging my Note 4 from about 35% or so to full one time. Not nearly as good as the battery bank.
The fuel rod does have some advantages up it's sleeve though. It is small, and relatively light, no big deal to carry. It comes with it's own cord for charging, and for the most part, you can leave it in your pocket (loose, cargo shorts pockets. Not sure I would try that with tight fitting pants) and let it charge with no problems.
The REAL advantage for the fuel rod, however, is the ability to swap it for a fresh one at any kiosk. In MK there are kiosks at Town Square in the Theater building, at Peco's Bill, at the big top circus gift shop, and at the power authority gift shop by Space Mountain. In EPCOT, at the twin gift shops (left one facing world showcase) International gateway, and the camera shop near Spaceship Earth. There are also locations at AK and DHS (didn't go to DHS, and didn't look for the one at AK) as well as Disney Springs (also didn't look for the location there) and all of the resorts. It is quick, and easy to swap the fuel rod out, and this gives you a fresh fuel rod with a full charge on it when ever you need it.
Because of this ability, we had no problem charging 4 different devices during the day in the parks. Also, if I happened to forget to charge the fuel rod over night, it was simple to swap it out when we got to the park in the morning.
There is one other advantage to the fuel rod, which again, has to do with the ability to swap it out. The whole reason I wound up buying the fuel rod in the first place is that my battery bank, after just two years, completely stopped working. It had never been wet, never been dropped or abused, it just died. I understand that this is the nature of rechargeable batteries, however, this is not a problem with the battery bank. Remember, you can swap it for a fresh one any time you want to, that means you aren't going to get stuck with one that no longer holds a charge, because you can simply swap it for another. This means that your investment is protected for as long as those kiosks are in the park.
All things considered, the simple ability to swap that little fuel rod out for a fresh one makes it a great deal, and a smarter choice than owning your own battery bank, as long as the company stays in business.