Before talking about the justification, what is the reverse flow reactor that enables the manufacture to charge $100 more for it?
Obviously, it is not simply reverse the powerhead's input and ouput, but unless you have have the specific make and model, I won't feel comfortable in making any comment.
Generally speaking, in reverse flow reactor, the calcium media is less likely to be compacted and affect the efficiency of the reactor. But for $100, there gotta be other design element that goes into it, such as auto start, etc.