Here's my seat replacement experience:
My original intent was to re-cover the original seat, but the original foam was mostly disintegrated, and the original seat frame was so rusted that the screws snapped in two. Since the aftermarket seats were so affordable, I went that route. I considered a solo seat, which looks nicer to me, but since the Benly is such a small bike, I felt I needed the room to stretch out on the longer saddle. When I ride my CA95, I tend to sit in the center of the dual saddle, so I'm glad I took that route.
The eBay seller was siam_motorparts1982, who has 99.0% positive feedback. I bought mine 2/29/2012 for $69.99, with shipping costing $79.99, for a total of $147.98. The seat looks fine, is comfortable, and the "Honda" stencil on the back is straight.