I did not get one for my first touring bike build, or the second.

But when I built up the third, I got the dynohub. In that situation, the cost of the rim is the same, cost of spokes is the same, and the cost of the dynohub after you subtract the cost of a non-dyno front hub is not very much more.

But once you already have a complete wheel, upgrading to a dynohub is a lot more than just the cost of the hub. There is the cost of new spokes, for some people the labor cost to build up a wheel. Although I build my own wheels, I just do not see the need to upgrade my other bikes.

Even after you get the dynohub, you then are looking at the cost of the USB charger. There are several on the market that have prices that vary a lot, along with quality that varies a lot too. I was a bit frustrated with the high cost of them, so I tried to build my own. But each time I went down a hill at about 25 mph, I would blow out circuits because my hub at that speed could pump out 34 volts if I was not drawing any current out of it. So, I ended up buying a USB charger/headlight combination that was close to $100 USD. The better USB chargers are $120 or more, not counting the hub.