If you look on the Steripen website, they link to a scientific article which compares various purification methods against crypto. The Steripen does very well in this experiment versus the chemical methods. The Steripen does just as well as heating (I guess that means boiling). As long as the water is not turbid, the Steripen seems effective.

"May not be designed for..." is not quite the same meaning as "does not work against...".

Well, that's just one study. I haven't tried finding any others that substantiate that claim.