Roommate has one and she uses both ends anally with no problem at all. She said you should just try it and do what is comfortable for you. She likes longer objects shoved up there, so she prefers the side with more bulbs.
I have one and have used the smooth end anally. I liked it and it works well for someone who is just starting out with anal play because it is small and with a little bit of lube it glides in very easily. I enjoy it for slow thrusting.
I have tried both ends anally and wasn't a big fan of either. The curved side felt like it was too curved too work with the shape of my body so it was a bit uncmfortable. The bulged side was better, but I would enjoy it more if it were longer and had more seperation between each ball.
Thank you everyone so much
If I got one I'm sure I would try it anally and just wanted to see if I was the only one or not! and I would have no idea which side to use haha, haven't used any anal toys (yet!)