I use a figure 8 with my 1/2" Arbormaster and it works. Lately I have been using the Rope wrench and find that it does not hockle or twist the rope.
Rope Wrench
Also I do not have to take the device off the rope if I want to go up.
Another descender that would work is the Large Petzl I'D Descender. It can handle 11.5 to 13mm.
What system are you using to ascend with?