They're not exceptionally hard to keep, or as hard as some make it sound. The gorgonian is a bit more challenging due to inability to easily tell how well it has been fed.
The terras seem to do exceptionally well with very fine powdered foods, like Fauna Marin Sea Fan and "F", soaked well in Selcon, Zoe, or the like. I also add frozen Cyclopeeze or ground mysis and/or a homemade blend, close to pureed. Definitely recommend using a Sea Squirt over a baster. The tip of a baster is too large to control feeding. Shut all the pumps off and SLOWLY squirt it over the terras. They close, making it simple to identify any missed heads. The "hardest" aspect is finding the sweet spot in feeding just the right amount to keep them fed while still maintaining NO3 under 10. Higher than that and they stress. With the gorg, I overfed and it spiked to 40. I knew immediately when it did, as the terras would not open. It took a 150% water change, over a week to bring it back down. Have since adjusted the feeding of all of them to compensate and am adding 2, 100g stock tanks (overkill but I will be adding the 135g dt to them as well). I generally feed them twice a night and they're thriving well, having spit off two new colonies in 6 months. The key is getting the squirt very close, rather than broadcast feeding them
They will want a large amount of flow. If they're not open during the day, they probably don't have enough. My Apex is on my other tank so I use an American DJ for the pumps. I can tell by looking at the terras, that I've forgotten to turn them back on!