[boost] [MPL] true_type,false_type versus true_,false_

I've been using true_type and false_type in some of my interfaces, for example: https://github.com/erikerlandson/edit_distance/blob/master/include/boost/alg... However it seems as though true_ and false_ are more compatible with MPL logic functions. Is there any particular reason to use one over the other? Would it be preferable to use true_ and false_?