I suspect that cdstan has bought the software by now.
However, I have used SLIDE and SLOPE/W and both seem to have similar features but sometimes dealt with in different ways, e.g. anisotropic strength functions, and one method may be preferable to the other depending on your requirments. SLIDE is however considerably cheaper and I found it much easier to use, particularly the CAD import / interface but then I was already familiar with PHASE2. Technical support from Rocscience (SLIDE) is excellent but I have not tried it with SLOPE/W. Both cater for reinforvcement and seismic loading.
I used GEOSTRU some time ago and it was good for the price. Although such cheaper programmes are adequate for simple analyses, check if they have the facility for Hoek-Brown parameters, probabilty, sensitivity, strength functions etc. if these are likely to be required.
With regard to "Garbage in-Garbage out", yes, elastic parameters are not easy to define but if you are using plastic analysis and Mohr Coulomb parameters with FE, these are the same garbage that you would input into limit equilibrium. As usual, it is horses for courses, sometimes limit equilibrium analysis gives more flexibility to analyse a particular problem.