I'm running 3.4 on 2 AC3's (non-pro). I agree that the new firmware is stable, but I've still been experiencing quirks (random 1 second alarm activations sending e-mails to my phone at the same time of day, but sporadic on days that it happens). This never happened with 3.3, and nothing was changed in programming or positioning of any devices. The other really weird thing is that I'm getting this on both controllers, but from completely different sources. On my main tank, it's from my low water level switch, and happens sometime within 10 minutes of the 2nd MH turning on. On the frag tank it happens when MH1 comes on, the heater turns on for about 8 seconds, and the alarm comes on for 4 seconds during that time. Fairly annoying, but at least it's during times I am always awake.