SCMS vs. RAS

As Brent mentioned, the control of the blade and depth of cut is a big difference in the safety if used properly. The RAS is essentially doing a climb cut, it's pulled into the work in a direction that makes the blade try to "climb" the cut. It's action if not controlled can cause injury as it comes toward the operator. The SCMS when used properly is doing something similar, but away from the operator. You can also control the depth of cut taken.

In theory, quality of cut can also be controlled as when cutting through a 3" thick piece of Maple using a RAS would probably get some burn marks. Making several shallower cuts with the SCMS would be less likely to heat up and burn.
 
If you make several shallower cuts with the RAS it would be less likely to heat up and burn also. Most problems of burning on a RAS can come from what is called heeling (where the head on the carriage is not adjusted perfectly straight to make the cross cut. There is a fine adjustment for this. Or a dull & or gummed up blade.)
 
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