During a trek this weekend into the San Rafael Swell in south-central Utah I finally had a chance to field test MSR's Miox purifier. And, I've got to say it's a dandy little tool, but it's not right for all occasions.
The beauty of this pen-shaped unit is that it's so lightweight you won't know your carrying its 3.5 ounces. The downfalls? Well, for starters it doesn't filter your water, so if you're not careful while filling a bottle prior to purifying it you could wind up with all kinds of interesting things floating around in your drinking water. Oh, they'll be dead and purified, but do you really want a meal in your water?
The second problem I noticed might simply have been operator failure in over-doing the purification. Whatever the cause, the water had a strong, chlorinated taste. Kinda reminded me of a two-tablet system I was introduced to when I first started backpacking way back in the last century -- you had one tablet to purify the water, and another to give it a palatable taste.
The Miox purifier works by creating an oxidizing agent. Basically, two batteries in the base of the pen send an electrical charge through a brine solution created with about one-quarter teaspoon of water that runs over some rock salt held in the cap of the device. You then pour this "cocktail," as the folks at MSR call it, into your water container and it kills all viruses, bacteria, Giardia and Cryptosporidium, a nasty parasite that causes diarrhea.
Now, I have been using MSR's Waterworks filter for years. The Miox purifier seemed intriguing because of its low weight, compared to the Waterworks' 19 or so ounces. I can see the benefits of the Miox if weight is a big concern (I've been sidelined from backpacking for about two years due to a bulging disk in my lower back, and now that I'm doing better I don't want to set myself back.)
That said, the aftertaste I encountered with the Miox is one drawback that perhaps can be rectified. Another drawback is that it takes four hours to kill cyrpto, a good bit of time you really don't want to wait if you are extremely thirsty. Plus, the lack of filtering sediment out of the water is another problem. Filters like the Waterworks take care of both problems at the same time, giving it a considerable edge if weight isn't an issue. Plus, there are no batteries to die, no salt to run out of, and the Waterworks filter can be cleaned in the field.
I have heard where some folks have gone to toting coffee filters or extra handkerchiefs to filter water prior to using the Miox system, but if weight's not a big issue, the Miox might not be the perfect solution for your water treatment needs.