I have been running the 3DN71 (XT grade, disc model) for about 4 years. It is reliable and trouble-free.
I can't say if the cones are thin, Ive never opened it up.
One of the disadvantages of Shimano dynamo hubs is the difficulty/danger of doing a standard bearing service. You can sever the thin connector wire that runs in a slot in the axle. My LBS (who are very good and built the wheel) don't like to open them. Some people have soldered repairs to this wire. I would like to see a Youtube video of a full service, the only dynohub ones Ive seen are not applicable to these versions.
I have the 36 spoke version, because it was the only one available in the country at the time.

I usually put the connector in the 7:00 position for a smooth cable route and to let it drain down.