I have two bikes with shimano 3n72 dynamo hubs. Absolutely cannot tell the difference. However, I have found that the hub might need a slight adjustment when new. From the factory the bearings are a little snug. Always adjust the non-drive side. The drive side, plug side has a little internal wire that you do not want to sever.

In terms of weight of the hub, I don't notice it when I'm riding. I typically carry the bikes to my basement for servicing. The little additional weight is no issue.