Seriously? You need convincing? Cmmmmmm
I've been using dynamo hubs for as long as I can remember (I'm in my 40's) beginning with a Sturmey Archer GH-6 (I think it was called) which only gave out a measly 1.8 watts at 6V.
It was enough to power a bulb that allowed you to be seen but not good enough to see much yourself.
Then came the Edelux headlight which was just "WOW", a few years back.
I upgraded to a Son28 which was a fraction of the Sturmey weight and put out a lot more watts.
I then invested in the new at the time technology of an E-werk and cache battery.
The E-werk/Son28 keep my iPhone 5s charged as well as my Edge 800 gps.
I then bought a Petzl Tikka 2 headlight torch for around camp which has a "Core" usb rechargeable battery which you guessed it is kept topped up via the E-werk.
I'm about to buy a Sony camera for my touring trips which once again is able to be charged via usb (take a bow E-werk/Son28)
I no longer bother with a car, so my bike is my means of transport as well as my recreation and means of holidaying.
My dynohub is my favourite possession and is used for some purpose almost every ride be it lighting on my trips to the shops or just keeping my phone topped up whilst I take a spin to the local beach.
I also keep a large cache battery for "just in case of emergency" but I think its pretty redundant as my hub keeps on top of everything as long as I'm careful with my prioritising the order of charging my items.
I'm only surprised anyone is unsure but then here in Australia towns can be many days cycling apart and having a charged phone could be the difference between life and death should one be involved in an accident/snake bite etc.
The sheer lack of thought with regarding remembering to buy batteries is really a joy.
In fact I'm so sold on dynohubs I built up a second dynamo hub wheel just for my Extrawheel trailer.
I can if you wish supply a link to someone who has added vanes to their Extrawheel trailer so they can turn it upside down at night and any breeze turns their dyno hub wheel (in trailer) and charges their stuff whilst they are asleep in their tent.
My iPhone needs around 4 hours riding to add a significant charge (from quite low to nearly or completely full) depending on speed.
Less charge on slow hilly country and more on flat faster roads.