I've been using my new PRO version for a few days now. And so far I think its working as expected. I have it set to 65f and my house temp could drop lower than 55f in the evening, but I checked a few times at night at it was doing a fairly good job (according to the display) to keep it close(ish) to 65f with the prob inside the existing thermowell on my SS BrewTech BrewBucket. Fermentation seems very very happy so far. While I can't really check this all the time, and the lack of a data-collection feature (maybe a nice improvement for the future) makes it hard to say for sure, but every time I check its usually only at worst the display reports its off by 0.3 at most (and I really appreciate the more precise display for this reason).
I would still like clarification from the Brewjacket folks to say how this should work and/or if there is any concern with the thermowell on the SS BrewTech BrewBuckets (or conicals which is about in the same position). But so far I think its doing the right thing.