The temp on the sous vide has to be higher, but holds the mash constant. When I tested with only water, it was only a 2 degree difference. Since this pump was barely moving the wort, I had to set it 7 degrees higher. I think when I get a reliable pump it will be about 3.
My mash temp was 150, so when I saw it drop to 149, I upped the sous vide a bit and it came back to 150 and stayed there. I was surprised how precise it was and how easy to control, especially with this pump ($24 Amazon pump the size of pill bottle).
I didn't step up to mash out because the pump was failing, so I am interested to see what happens on big step mash changes. That is where I will use the induction cooktop. What I have noticed, testing with water, is that the temp moves up pretty quickly, then I shut off the induction cooktop and it takes a few of minutes for the sous vide to stabilize the temp in the pot. Initially, the temp drops a degree then works its way back up. Overall, I'd say it is pretty precise.