There was another thread about this someplace (Dootalk maybe). A couple people that had bought the double axle said it bounces more then the single and tows pretty much identical. One guy had owned both. Had the double axle for a few years and then traded it on the single.
Only advantage I could see for the double would be if you were going to insulated and finish the interior and wanted the higher payload for that maybe?
It seems like most people are ordering these single axle hybrid inlines without brakes, due to the competitively low weight. What made you go with the brakes? I think that’s the way I would go as well.