I am not an electronics expert. But I understand about ionization. Clean water can act as described depending on the sensitivity of the sensor...the two metal plates. This is really not the common cause of failure, I don't believe. I'm not very well versed on the sensors in the adventuror, though. It could be true, though. I'm sure that a higher electrical drain will keep stuff warmer. So, a little salt will help, but not for the reason cited. The sensor should allow operation with most any ground water. I have not tested it, but distilled water will likely work.
More likely is the temperature of the water. The heat traveling out of the electronics will have a rather negative effect on it's operation. Near freezing, you might not get a complete cycle. The heat generated from the circut may not keep up with the heat lost, soo, at low temps, it will not turn on or dies early. This HAS happened to me. Switching out to new batteries did not help. It starts, runs fine for a few seconds and dies with a red sensor light. The batteries were kept in my pants pocket, so, it was not cold batteries. But, the water source was at 32F (it had some ice in it.) Not conclusive, but, highly likely that it got cold during the treatment and turned off as if it was removed from the water, due to the low current draw induced by the low temp. The metal conducts heat away from the electronics far more efficiently than the optical sensor of the Opti.
Anyway, when I got back, everything worked fine, even the old batteries. The water was much warmer, too.
Soo, offhand, I would say that the Opti has a couple distinct advantages.
1) Less idle current draw. Sort of irrelavent, just flip the top battery to kill all current drain, Opti or Adventurer.
2) Optical senser. This makes it immune to the effects of intermittant failures. However, the lamp output may vary with temperture. Keep it in a warm pocket about 15min before using it. This is easy, since you have to get the batteries warm, anyway.
With the 600ml bottles I use, I keep it in my pocket between uses in colder weather. Note that most chemicals don't work that well in water below 40F, either. The speed advantage remains. But, if the gadget gets cold, you could end up with a dead unit again.
Like anything with batteries, camera, cell phones, SPOT, GPS, readers, etc, you cannot let them get much below 50F and expect 100% of normal operation. More than the batteries, the actual semi-conductors can be adversly effected.