I often wondered what it felt like for my wife when I penetrated her and decided to give her dildo a try on myself. This was me by myself, my wife didn't know or participate. Started with her metal vibrator which is really small and it went in like nothing and felt like nothing. Then I tried her 6" x 6" and that took some time, but still didn't do much. Later I pulled out her biggest one. This is a massive 9" long dildo (only 7" is usuable because of the balls), and 6 1/4" of girth from top to bottom. Took quite a while to get it fully inserted and to the point where I could do whatever I wanted to myself with it.
As for the so called nerve endings around our anus, mine must be dead, sleeping or missing. Nothing like my wife going down on me in regards to how it feels. I did get off mostly because I was actually pounding myself with this thing, and because it was such a "dirty" thing I was doing to myself. So for me it was more of a psychological turn on then it was a sexual turn on. I did get off fantasying while putting myself into different positions and seeing myself in the mirror, but again, I didn't really physically feel very much at all. I have used it multiple times since, but not lately.