With my 4 AP cages, I have the Flexwatt anywhere from 105-112. They are larger cages than yours and stacked on the same side as the RHPs, thus the range differential.
If the second probe and t-stat help you sleep better that’s fine, but unnecessary. Most folks check those floor temps daily with an IR temp gun found on the net for under $20. I saw one at Tractor Supply yesterday for $13 and almost bought it. But I already have 4.
As far as toxin release, I don’t know. There are a lot of unknowns with plastic all around us and some known facts.