HERMS and RIMS are two different things. In your application, a HERMS rig would be more beneficial to you since you don't want to directly fire you mash. You wouldn't see a whole lot of upsides from it, but it may cut down and hot/cool spots in your mash since you're continuousy recirculating through your heat exchanger.
In the end, I think you'll like having a controlled temp. The nice thing about using a cooler, is you only need to have two burners on a single tier stand. And only one of those burners needs to be controlled. The only downfall to not having a heated MLT is that it takes a bit longer to brew. You would need to heat your strike water in your boil kettle or HLT, then transfer it. I have a HERMS rig, but I also have a burner under my mash so that I can heat my strike water.