As msn says, take reviews with grains of salt.
I reckon failures mentioned are more of a hardware issue, ie broken, that's what I took from negative accounts, and why I was careful of mine in use and transport. I know there are lots of people who are bull in chinashops with stuff.

Re actual filtering. In my travels, I was very careful with my process. I put water into my large coffee mug, maybe 350ml, and the steripen wand could reach near bottom, and I could stir easily. Would pour this into my bike bottle or my spare store bought 1 litre and 1.5 litre plastic bottles, repeat until full.

I've been sick before traveling in Latin America on my own in the past, and frankly my dear, it's a real Chitty experience, and had no urge to revisit this while bicycle traveling....hence being careful as heck and being attentive to what I was doing.

You can't control everything, but this is one I could.
You can always have bad luck with food (I ate always in small roadside places, family run usually) but you can do your best with chosing places that look ok (not always had a choice, but hey)