I'm an old-timer and I began doing S&M sessions with Mistresses when I was 20 or so. My first Mistress wanted me to get used to wearing a butt plug during a session and when I went home. The sensation was like I had to... go to the bathroom. A year or so later a gorgeous Mistress advertised "reversed rape" or some term like that. Me being, looking back at it now, an innocent and / or idiot, I thought that meant, "Wow, she's gonna pin me to the bed, get on top and fuck me." Ahh... no. Again either a butt plug or strap on was involved. (It was so long ago I forgot which.) Anyway, the discomfort of those two times got me out of ever having a full strap-on experience.
However, as I got older, Mistresses and female bodybuilders have violated me with a gloved finger or two, and even a small butt plug. I'd almost like to try a strap on session now, but given my age and lack of flexibility down there, I'm not going to go down that road.