Re Wikstromwrote a review of Hydro Photon SteriPEN Ultra on May 16, 2017
Familiarity: I've used it several times
A friend brought this along with a multi-day ski tour in the Eastern Sierra. We also brought enough jet boil fuel for the 4 days, ended up using less than half of that fuel since we found enough running water.
In an alpine environment where you have access to clear water, this SteriPen was SO AWESOME to have. So easy to use!
There are some people who would argue the water was probably clean enough to drink without treating, but when the Steripen is so small, easy, and quick to use, there is no need to take chances and worry.
It works best in a wide mouth nalgene. I also had a platy bottle with a much smaller opening, so I would treat the water in the nalgene, then pour it into the platy bottle. Then refill the nalgene and treat the final liter.
For hiking somewhere like southern Utah where the water is a lot siltier, I would suggest something like the MSR Guardian Filter instead, but when you have relatively clear running water sources, the Steripen is where it's at.
I have also heard of many friends using it for travel to treat questionable tap water and avoiding sickness where their other friends did not.
Quite the handy little gizmo!