Classtime 

I ordered a M1 from Japan and then was informed that shipping would take forever so I cancelled the order. The M18 which seems to be widely available in US is now under consideration. The rack will sometimes go on a Trek 620 with low rider brazeons. And sometimes on another bike with brazeons at the drop outs. Either way, I will get longer struts and attach at the fork crown also. I intend to luck out on an Acorn Rando Bag later this Summer or Fall. I was about to order the M18 but thought to check here first if there was a good reason to wait for the M1. Under what circumstances might I wish that I had Mark's Rack instead of the M18?