I don't have an M18 (i actually need one too), but I have this SOMA rack that I recently prchased in its stead, but didn't work. If you're interested and think it could work for your application, I'll give it to for you a bargain;
In my case, it didn't work because it interfered with my Paul Racer centerpull brakes. It sits slightly lower than the nitto racks due to the shape of the diving board. I tried it with a nitto diving board that I happened to have, but then the struts - which are fixed-angle - didn't end up in the correct location. I'm kind of bummed, because it would be much more sturdy than the nitto. The fixed struts and thicker diving board are improvements if it fits. I'd be comfortable with a much bigger load than on the M18