Despite being pretty squeamish about the thought of them, I'm slowly being sold the idea due to the leakfree-ness (not a word, I know).
The only major concern i have is, what if you need to change it when you are out and about. If you are in a public loo (with cubicles and a bank of communal sinks) I assume you pour the bulk of the blood into the loo pan, but what about rinsing it out ? How do you deal with it ? I'd be horrified if I was stood at the sinks and some woman stood next to me and started washing her menstrual blood down the sink.