I can't help but think that you need to figure out how to budget for the ancillary stuff you need when you invest in something like the Behmor.
Most purchases require support stuff.
It's part of the cost even though you have to buy it separately.
If you don't have the testers to know what you are doing, having the toys in the first place doesn't make a lot of sense.
If it turns out that your voltage is too low, of course, then you are going to need (a very expensive) Variac to do what you seem to want to do (overcook your beans).
You might have done better (and maybe could still do better) to build yourself a SC/TO with which you can probably roast as dark as you want and as many beans as you want.