Well, I read most every page on the Nova thread, and a number on the fx thread. I also read most of the amazon reviews on the Herboven too (and a few others).
I'm still on the fence with them.
I have a lot of hobbies going at the same time, and I've been having some success using a crockpot to maintain temps around 90F. I bet I could do the same at around 250F for decarbing shatter. The thick ceramic pot really holds heat and balances out the temps inside, preventing much fluctuation.
The key for me is using a variac. With the variac and a temp probe I've been able to fine tune the crock pot for a consistent temp. If I can get it to plateau at 250F and stay there, then I might try decarbing a gram of shatter in a small pyrex dish.