I would say my main reason for herms was I was planning a element (w/ pid control) in the HLT anyway, so why not make full use of it and run wort thru a coil in it? I have 3 vessel set up with just 1 PID (auto for hlt, manual mode for BK). RIMS seems more suited for when you are running propane/nat gas for bk/hlt.. and just use electric for rims.
the second would be, the RIMs set up brings a bit more risk to it in my mind, if I ran into a stuck sparge, the wort may over heat causing massive pressure build up, if the temp sensor is on the rims outlet, and flow stops, you are in trouble. so you are looking at a more sophisticated set up with flow sensors, etc.. if I get a stuck sparge with a herms set up, there is no risk at all.
just my opinion for what its worth