I ordered these traps when it emerged we had mice in the kitchen in my student house (not surprising really!). After reading some of these reviews I was a little skeptical, noting that the traps needed to be modified before they would work effectively. I took the plunge and bought them anyway.
When they arrived I saw that the plastic trap-doors were indeed a little bit too light to snap shut effectively, so I took the advice of other reviewers and weighted the doors by blu-tacking a 2P coin to the outside of each. That solves the problem completely.
They were placed and baited with chocolate, and within the week we had caught our first mouse! We let him go unharmed (sort of defeats the idea if you don't), and another followed a week or so later. So far, so good!
It's a sad fact that humane traps, being more complex in nature and having to catch the mouse alive, will never be as cheap or effective as conventional snap-traps (or, if you're really sadistic, glue-traps and poison). Fortunately these provide a cheap and easy alternative that works well, if not as well as a snap-trap.
All-in-all, I'm really glad I bought these now. whole-heartedly recommended!