If you want 500-600, I would definitely consider a MAG 18. It worked well for me for a long time. If you look, you can usually find them new for just a little over $100. A wahoo is going to cost you 4 times that much.
And you are right about the heat transfer, I noticed my temps drop a substantial amount when I set up my basement sump...even with the MAG 18 running. That is just heat you don't need a heater for.