SteriPEN Journey Water Purifier System
UV purification is a genuinely clever idea and the review captured the appeal: no pumping, no waiting, no taste, and about 90 seconds a litre. The SteriPEN brand continues under the Katadyn group, though this exact model has been superseded.
What UV does and does not do. It scrambles the DNA of viruses, bacteria and protozoa, which covers essentially all the biological risk in fresh water. It does nothing about silt, chemicals, heavy metals or taste, and it only works in water that light can get through. Cloudy water must be pre-filtered through a bandana or a coffee filter first, or the UV cannot reach what it needs to.
Where it beats a filter: travel rather than backcountry. Filling a bottle from a tap in a country where you do not trust the tap is exactly the use case, because it is fast, it treats viruses that many hiking filters do not, and it adds no taste at all.
Where a filter beats it: volume and silt. A squeeze or pump filter deals with cloudy water, needs no batteries, and treats a group's worth without waiting.
The real weakness is power, and it has not changed: batteries, in cold, at the moment you need water. Current models are USB-rechargeable, which is better than the lithium cells this generation wanted, but it is still a device that can be flat.
So the honest recommendation: carry chlorine dioxide tablets as a backup regardless of what else you carry. They weigh nothing, last years, and work when the clever thing does not.
Part of the guide to water filters and bottles.