In a large HLT with a large volume of water, pin point accuracy isnt really a concern I have found, because you have a huge thermal mass buffer in that HLT water.
Bottom line, running my HERMS on a JC A419 gives me mash temp control within .5F during the mash. Id say that is pretty good. YOU ARE limited to 1650W on the JC A419 though, but I have had no problems with it.
Also you DO NOT need a low density element for a HERMS, it is heating water... can't scorch water. You can use any HIGH WATT density element, I actually recommend that. They are shorter, so they take less HLT water to keep them submerged.
I have been over this and over this...
1500-1650W high watt density element
JC A419 controller
It is easy, cheap, effective etc. Look over my build threads, if you have any Qs let me know.