The HV attys don't take off any volts. They are just higher resistance. I really wish he would change his description. It's misleading.
Just read up here if you want the details of why I say that...
http://www.e-cigarette-forum.com/forum/nhaler/57002-high-voltage-atomizers-2.html#post894154
But... the 5+ ohm HV attys are able to handle the 8.4V that will come from two 3.7V 16340's. I have several custom 801's (not nhalers) that are made specifically for 8.4V vaping and they hit like a freight train.
While the Nhaler (nerf) attys aren't quite as good as the ones I use, they are still a better hit than anything using less than 8V. You better stock up on juice though, cause they get really thirsty at that level.
...and I would not recommend using any stock attys at 8V. 8-o