i have a one year old female GT and she has never shown any aggression. i have heard that adults can, but again i believe that's based on how they are handled. imho if you handle your animals early and often, you will have less of a chance of an aggressive adult.
I would say do a broader search. I've seen some vids of cage/tub agression, but the moment they were out they were fine. This is all based on what I've seen of other people's leachies.
I used to have a decent sized collection of breeder leachianus and I have only seen them show aggression towards each other, never had one be aggressive towards me that I can recall.
Through my experiences I've only found leachies to show aggression when in their enclosure. After getting them out, they hardly ever continue their aggression. I think it mostly has to do with a territorial responce. Or if you happen to startle them when they are sleeping.(i.e just picking them up while they are sleeping).
If you handle them at a young age where they get used to coming in and out of their enclosures I believe you won't have as many or any problems.