I’m a wrasse lover and Leopards are my favorite - I currently have 2 Leopards and 3 other wrasse. I’ve never had an issue with internal parasites.
@Dr. Reef puts them through a complete quarantine treatment process, longer than 14 days, then an observation period afterwards (so be prepared to wait, and wait). You do not need to re-quarantine them. It is definitely worth the extra cost. There is no guarantee that they could not develop internal parasites afterwards from other fish though.
Having said that, I do not recommend adding them to a newly established tank. The biome is not yet fully developed, nor is the pod population, and water parameters are not yet stable. 6 months would be the minimum time I recommend.
They are not a feed-twice-a-day-and-forget fish. Their metabolic rate is set for grazing all day so a heavy pod population is a must. DRF makes sure they are healthy eaters before shipping. The ones I purchased from them were even eating pellet and flaked food, which is rare for most leopards, but that is just to supplement their normal pod diet.
LOTS of matured live rock is a must for them to graze. In fact, a refugium is also a must unless you are cultivating your own pods. Restocking pods will get very costly otherwise. They require a minimum of a 3” fine-grain mature sand bed (6+ months). Some people just keep a small area of the tank deeper, but sand moves overtime, so that is not something I recommend. It also seems cruel to me - like keeping a dog chained to a tree.
I hope this helps!