I don't understand the difference between water purifiers and water treatment systems.

REI sells many, many systems, including purifiers, most or all of which I asssume are effective...

Probably most of the foremost researchers in this field, including Derlet, Rockwell, Zell, Welch, Backer and others, question whetherr water treatment systems or purifiers............. are worthwhile or justified in deep wilderness.

You can verifiy these various opinions and the credentials of these researchers by searching their names on Google accompanied by "wilderness" and/or "water treatment" I'd guess. Sometimes, you have to read their stuff with some care...Whatever, It's all out there on the Web.

Hikes in non-wilderness areas, like much of Appalachian Trail, for example, might face a somewhat different question.

Personally I've consumed a lot of untreated water in these non-wilderness areas over several decades............with no ill effects.......... But there is apparently no telling whether you might actually get hepatitis........To say nothing of more minor troubles.

I've got a PUR filter which I've used somewhat rarely and randomly....and is apparently NOT a purifier..........I think it weighs 11 ounces............I'd guess it's effective, and I know it's a slight pain.......