Well right now I have 2 gr-modders rings and 2 hippos. looks wise I like the gr rings, but when I am using my tatroe tanks, I cant get them to contact the battery easily, I had to pull on the bottom pin a bit, with the hippo there are no issues, with the connection, but it seems like my coils fry quicker when using them. I could be wrong about that, mabe the coils were about to go any way. I have never used a carto so I don't know about those, but I just got a kayfun lite, and the hippo looks, and works great. ( if I could get the coil build down right)