Bergia work....period. That noted there are some conditions which must be met for them to live and consume the aptasia. On that note, think about it. Bergia eat only aptasia. That is their only food and their diet is exclusive to aptasia. No aptasia and they die out quickly. Also the aptasia x and joes kill the ones you hit, but my experience is for every one you kill within weeks 5 new ones grow out.
Anyway.....for the bergia to work, you need all wrasses and peppermint shrimp gone. Period. One wrasse or peppermint will wipe out 30 bergia s in a day or so. Even the leopards. The peppermints wipe them out almost as fast and worse they hit them at night when the bergia are active. I have a coupe large tanks and one had a few thousand aptasia at one time and learned this process the hard way. I placed 25-30 bergia each time. Each time I lost bergia to peppermints that I could not catch, then to wrasses. I ran interceptor to kill shrimp and caught the wrasses. Then the wrasses need to stay out a couple months until the aptasia is gone. Last is the water perameters......need good water. High nitrates will also kill the nudis.
Get these right and there is zero chance the nudis will fail. Fail in any of these perameters and the nudis are simply dead one way or another.
Last is the number you need and how to place them: five is fine for a small tank or a few aptasia. I was working with 25 at a time in one tank and about 12 in another tank that only had 50 or so aptasia rather than 1000 or so aptasia. If you hav e only a few nudis in a large tank they can simply die of starvation before they find them all. When placing shut pumps off. And place them NEAR the aptasia, not on the aptasia. If you place them on the aptasia they will actually get stung and/or eaten and again, they are gone.
Do it right it is a natural fix, but it takes time and all of the above to be successful. On a positive note if you have a lot of food for them in less than a week you will see nudi eggs and they will reproduce in your tank if they sense there is enough food to support a larger population......