It's a very tough coral to keep alive, especially the long green ones that they sell at sunflower coral. It's really hard to tell if it's doing well, as in the beginning it's fully open and look like it doing great. This usually goes on for a number of months, then around 5 -7 months it starts to lose tentacles and then all of a sudden it just dies. Most people think it's from starvation, though I don't think anyone really know for sure. Some new food has just come out, specifically for Gonipora, but I'm not sure if that's what they need to keep them alive or not.
The ones that I currently have in my tank are the type that seem to do the best, Red with Blues eyes and Gray with Purple Tips. I also have Alveopora, which is hardier and seems to make it. I have mine on the bottom of the tank, on the sand, with not a lot of light or flow. Most people that have success with them have a lot of flow on them and towards the bottom of the tank. The only people that I know that had success were at gonipora.org, though I'm not sure if that web site is around anymore. They actually not only kept them alive but had growth too. The Red one from ORA seems to actually grow, so there maybe hope for keeping this coral long term.