Because of the lack of a bulb we've had these firmly in the "good for use in a harness" category, but it seems like it's just too easy for it to slip out to be used without one. This might just be a body shape issue so:
Can you hold your Vixen Nexus in without a harness? If so is it just some positions, and how does it "lock" in? I'd like to hear from both those who can and can't.