i did a comparison of the two programs a while back and found that if settings are adjusted properly the two programs give basically the same results. The main things to examine are the fixity and modeling of columns above/below your slab and what the datum is for lengths of columns above and below the slab. The two programs generate meshes a little differently. SAFE gives a more control of meshing. If you are already familiar with the CSI programs the SAFE interface will be more intuitive. I have problems useing the Concept interface b/c i have spent so much more time with the CSI programs. The selfweight calc is a little different between programs. I recall one of the programs is more conservative than the other. Same with punching shear checks. Both programs have issues with the differentiation of beam and slab shear where those elements overlap. Spend the time to understand this in either program.