What are the advantages of having a spinner luggage that has dual wheels (so 8 wheels total)? I'm interested in getting a carry-on sized spinner luggage that will be able to fare ok "off-road" (in the dirt/grass/uneven pavement) and was considering the Eagle Creek here: http://shop.eaglecreek.com/no-matter...CategoryId=113 since the wheels look more robust than other spinners. But I wasn't sure if a spinner that has 8 wheels would be better as this only has 4.

The other bag I was considering (which I know is in probably a different class range considering the cheaper price) was this one here: http://www.ebags.com/product/it-lugg...uctid=10469720
I'm never going to be checking in these bags, so the durability doesn't necessarily matter (as long as it doesn't just break under normal use). I just want it to be able to roll fine in various terrain.