I bought this as a possible replacement for my Katadyn simply because the replacement filters are so expensive.
The Mini is made to screw onto the MSR Bladder or the Nalgene bottles, then you screw the filter onto your bottle, pump, unscrew and drink. Simple and effective and no need for an exit hose that is always coming free and falling into the mud.
My main complaint is that the Mini is designed to screw onto the top of the MSR, Reliance and Nalgene bottles. As I had a brought a few off-brand bottles, I found that, in the field, the openings and threads did not match! AS I am unaware of any adapter for the hundreds of knock-off bottles, if you buy the Mini, be certain to take ONLY Nalgene and Reliance bottles with you.
This is why I gave it a 7, the requirement for a specific water bottle when many of us bring the ones we are given as gifts by companies seeking our business.