I have had my share, LOL.
For me, there are two things besides the size, that made it different for me.
The first is the intensity they tend to have. While I like my blk men charming and well-dressed, once the clothes are off, the intensity goes up to 11. Sometimes the way they hold your hips is just so strong, you feel almost helpless. It's a weird feeling that's hard to describe.
(you are welcome to DM me if you want more details)
The second is the fact that your husband is watching or knows what's happening. The first time my husband was 6 feet away on the couch getting a bj from the other wife (it was a swinger set up more than a cuckold). Something about looking at Mark, then Steve, then Mark again and Steve (my husband) loving every minute. It just made that "bad girl" in me come out.
The size does take a bit to feel comfortable especially if he is longer and thicker than your husband. If you have a vibe that big, it's not a big deal. I didn't. Most of my fun by myself involves a well-placed anal plug and my finger going in figure 8's in just the right place.