Careful with the lemon juice if the aiptasia is anywhere near a coral, it's easy to damage them. I've had good and bad luck with the lemon juice depending on what is nearby. The aiptasia x works well if you can get it right in the mouth. Aiptasia have a knack for growing where I can't reach them on the bottom of a base rock.

The group buy of berghia nudibranch was a little over a month ago... maybe they'll jump in with some feedback?
I would be interested in trying a few if I heard first hand experience of the effectiveness. How many does it really take to get the job done? They're pricey, and they may breed?