I use Merkmatics Chess Clock which I think I paid $0.99 for. It functions great as a death clock, large numbers in the display, easy to read and use. The app, however, is not ideal for timed turns since it is just a chess clock. So, I basically have both players play out their turns, then I reser the clock for the next set of turns. I dont know how easily other clocks do both timed turns and deathclock, but something to think about.
Thanks for making this, I am looking forward to seeing it!
Warmachine - Cryx, Khador