Re: Traveling with your MB...
I've used strap on racks several times to carry mine. While I agree it's less ideal than carrying the bike inside or using an under the wheel hitch type rack I think it can be safely done. The step most people fail at is checking the straps AFTER the bikes are loaded as the weight of the bikes on the rack can make formerly tight straps become lose. I also check the straps EVERY time I stop (for gas or other breaks) just to be sure they've not worked themselves loose.
That said, I'd still use one of the other options if it were available to me.