I think they would be great for low impact, low speed use on sandy surfaces, but I don't know about running them on MB.
For $40 each, I hope they have some guts! I plan to try some sometime on a pedal bicycle, probably a rainy day beater or fishing bike.
A guy named Duct Taped Goat (banned) said his wore out and fell off.
Some people swear by these though, so I guess time will tell if they are a hot new trend or fringe market.