Ahhhhhh the Melichthys Species (Indian, Durgon, Pinktail)
when you combine the Melichthys Species with lions, there is always a risk.
My personal experience has been great with this combination. I have had my Pinktail for a few years now and I keep it with my lions, but I offer this trigger space, I allow room for him to establish it's own territory, it is an adult and can have mood swings but usually just at night.
However, I have read some pretty bad experiences with the combination (Melichthys & Lion) over the years, so it will depend on the fish, I have also seen these bad experience more with the Pinktail than the Indian or Durgon.
Personally, I would say go for it, your tank is 240g, and just watch it, keep an eye on your lion fins, if you see spines being nipped, remove it. Ask your LFS if you can return the trigger for a full credit, if things do not work out.
My favorite Trigger, My Pinktail
Moody, Moody!!!
A little risky, Yes, but Huge mistake, No.......