I like to have a butt plug inserted when having sex as it enhances the sensation when I cum. The problem is it keeps falling out. To help stop this I have tried wearing crotchless pants that I bought on LH but even then I'm struggling and to have sex whilst holding the plug in is not comfortable.
The slender neck relative to a larger head helps give a firmer grip,
Also, the long neck also means that the inner ring of muscle of the anal sphincter (think of it like two cock-rings stacked) can close behind the head of the plug, so both sets of muscles are gripping tight. Many shorter necked toys can hold the inner ring, or both partially, or fully open.
I love the feeling of a butt plug in me while having sex and it helps me shot and feels a lot more intense as a guy. I have also seen many girls like it at you can feel it while having sex presses against spots that help them to finish it’s something I have talked to my girlfriend about. Personally I think it about trying different sizes not just in length but also width and shape. The material can have an impact my silicone one came out a couple of times but I love my glass one and it sits nicely in place