i had 2 experiences with Berghia.
My first was probably ill-fated from the start... If I remember correctly, I purchased 2 from a local reefer, which went into the rock, never to be seen again and no results. With experience, I would never recommend less than 3 (in case you lose 1, they can still breed giving you a second chance).
My second was better thought out. I was lucky enough to get in to a group buy and bit the bullet, getting 15. Very scary thought considering my first experience. This lesson was going to be much more expensive. I setup a QT tank and pre-seeded it with aiptasia I scraped out of my DT. I received the Berghia about a week later. Was glad to have the very low flow QT setup! The shipping process takes a lot out of them. I think if I had put them directly in my DT, I would have large loses as I'm not sure they would have had the strength to hold on to the rock. As it was, they went into the QT for about 4 weeks, gaining strength and size! I have a fellow reefer to thank for this wisdom.
While they were in the QT... they were breeding, and a few weeks later I was able to add more. But the initial 15 went into the DT... and they were breeding as well. So I did have many... and have gotten new homes for most. I still have 1 or 2 crop up suddenly.
This process wasn't all good times though! After putting the Berghia in the DT, 2 months passed, and I had never seen them again and did not see any results... then within a week, suddenly I had both results and Berghia visibly working on the rock... from complete failure (or so I thought), to what looks like a great success!
I will say again though... I would try cheaper means (if the problem isn't too bad), before going this route.