I just received a oneTeslaTS coil for Christmas.
It took several hours to build but I spread it out over 3 days so it wasn't that bad.
Although I tested it in stages per the manual, doing the interrupter test, low voltage test and then high voltage, during the high voltage test, I noticed smoke coming from under the torroid. It turns out that I burnt a nice long carbon track on the inside of the coil. Once you have a conductive path, unless you grind it out, it will keep arcing in the same place. In trying to fix the coil, it appears I broke the winding in the center.
So now I had to order another secondary coil.
The moral of the story is be gentle to the hairlike wire on the coil.