I occasionally play with these things, nicely lubed up, in 8 and 10mm widths, which is not so much for this kind of behaviour... I have seen things which make me want to scream, though some of you will look at that and feel the same way...
The feeling varies depending on the day, but is usually very intense and extremely erotic but not something that's likely to drive me to a satisfying climax on it's own.
Caution is advised, I've let it slip a couple of times - lubeyfingers - and the weight can let the taper slide down inside far enough to freak me out a tad, but it's easy enough to push it back up...
I have friends who've been sounding (we know it's called sounding, right?) with TENS machine electrodes and other such devices. Interesting.