They do not make much power. They last a long time so ideal for space travel or in volcano sensors where you cannot change the batteries. No good for cars or houses. Lithium shares are safe 
Yep, I realised after my first "Wow" reaction, that the available power is all you get from carbon 14 decaying.
So power to weight won't be very good.
I guess the power is created 24/7, so higher power may be available in short spurts, when the device has "charged itself up"
Cost also isn't mentioned!
It will be very interesting to see what actually happens with it.
