You can get away with keeping puffers and lions together, it just depends on the individual fish and tank size. I keep a dogface with my lions in my 300g, I also keep a close eye on their fins
If I see any signs of nipping than I will remove the puffer. Puffers can be nippy in return lions can sting the puffer.
I also feed my lions on one side of the tank and my puffer on the other, overtime this has worked out great for me, and it helps avoid accidental nips and stings.
Kaye